For equally thick blades, blade metal probably plays the largest role in supporting the cutting edge when comparing geometries with slight variations in support angles and contact heights. I bet a step up in metals is the best thing you could do. And a better metal will stay sharper longer. But this statement is vague and requires investigation. Ron Hock thinks High Carbon Steel takes a sharper edge but that A2 is usably sharp for longer. If this is true perhaps use a high carbon steel blade on your final smoother to produce the best surface but A2 blades on your other planes to reduce sharpening frequency. And then there are the high speed steel M2 blades to consider. There are also laminated blades that take advantage of the stiffness and toughness properties of two different metals. Steve Elliot has a great website that looks into these details. Hopefully he will be able to answer more questions about different metals and how they work for plane blades.
Thicker blades may give better performance and manufactures of high quality planes use blades thicker than the 0.080" Stanley blades. It could just be marketing but that is not what users seem to think. I presume that the increased contact height of a thicker blade is not a serious penalty to pay for the increased stiffness of the thicker blade. This suggests that for thinner blades, blade vibrations along the length of the blade are a larger problem than vibrations in the cutting tip of the blade. The thickness of the blade is so important that Steve Knight's 1/4" blades apparently give incredible performance even with a large contact height as he uses a single bevel.
In a rec.woodworking post Jeff Gorman pointed out that the flexibility of thin blades in metal planes may make them easier to press tightly against the sturdy metal bed which can supply the rigidity. I think that if the blade and bed are both as flat as we can practically make them then this is not a factor: the blade will not need to flex in order to make good contact. (But to be fair, perfectly flat surfaces are difficult or impossible to produce.) Also Jeff suggests that thick blades in wedged wood planes may make up for a lack of pressure supplied by the wedge pressing the blade against the less stable wood bed. If this is true then I think in any plane a thicker blade must help improve overall rigidity. But for a particular plane and task and if thicker blades do perform better, above a certain thickness performance will not improve but sharpening time will increase. That is, there will be a blade that is thick enough to do the job and thicker is just over kill.
I think that the problem with thin blades isn't the blade itself. A thin blade held securely by the bed and cap iron would not vibrate along it's length and chatter. Also the thin blade will have a lower contact height and smaller tip so if chatter is a result of vibration in the tip then this would be reduced too (along with sharpening time). I'm not advocating getting a thinner blade because experience shows that thicker blades perform better. This points to the possiblilty that the standard methods of securing the blade in the plane could be improved for a more stable blade. A new cap iron might be a step in the right direction.
Ron Hock sells thicker cap irons and his website states "To maximize your plane's performance, a thicker chip breaker (cap iron) can stabilize the blade's cutting edge reducing vibration and chatter." Lie-Nielson also sells thicker cap irons and their site says "A big part of a chipbreaker's function is to dampen vibration, but chipbreakers on metal bench planes are usually quite thin." (Diagnosing chatter) If the majority of vibration causing chatter occurs in the tip of the blade then this could all be marketing. The actual roll of a cap iron in plane performance is heavily contested. It definitely transfers the lever or wedge's pressure to the blade and presses the blade against the bed. Some people think the cap iron also breaks chips, some think it pre-tensions the blade to avoid chatter and some think it is just an obstacle that gets in the way to help eject the shavings. If Ron tested his cap iron and it improved performance then I think that the cap iron must do more than just get in the way to help eject the shavings. Steve Knight doesn't use a cap iron with his 1/4" blades, which apparently never chatter, and that leads to the conclusions that one of the cap iron's roles is to supply rigidity to thiner blades. So a thicker cap iron could solve a chatter problem.
Steve Elliot has a lot more info about the function of cap irons as chip breakers.
Lee Valley's Veritas bench plane frog extends all the way to the sole of the plane. For a 30 degree single bevel on an 1/8" thick blade at a 45 degree bed angle set to take a light cut the contact height is just less than 0.0915". (The contact height is 0.0915" minus 2 times the depth of cut.) For 0.0458" deep cuts the heel would be flush with the sole. For continuous blade support and an adjustable mouth opening the frog only has to get close enough to the sole so it supports the blade to the heel. It does not have to go all the way to the sole. But the Veritas frog is still a great idea and makes the mouth opening adjustable with continuous blade support.
Lie-Nielson and Clifton make planes based on the Stanley Bedrock design. From what I know, these beds support the blade all the way to the heel and make the mouth adjustable. I haven't held one of these planes but I think this design could support the blade all the way to the heel even if the heel is below the sole. But this would be a very large depth of cut. I don't think you would ever use a depth even close to this large or be able to push the plane. For difficult grain, Lie-Nielson also makes an optional 50 degree frog for some of their bench planes.
Wood planes have fixed beds that support the blade all the way to the sole. On some, the mouth can be adjusted by other means. You can make or buy these. One nice feature of wood planes is the blade can be bedded at a range of angle.
In Jim Kingshott's book Making & Modifying Woodworking Tools he describes infill planes as the Rolls Royce of planes. In some, the bodies are not made from castings so the latent internal stresses of cast parts are not a problem that later warp the plane. So the long wearing steel sole will stay flat longer. Infill planes have continuous blade support but the do not have adjustable mouths. From what I've read the mouths of the smoothers are opened very little with a file to take fine shavings and that's it.
Excel worksheet for the calculations in the tables.
Feedback? Questions?