I don't think perfection means taking a 650b wheels and putting them on a bike that takes a different size wheel. KHS and Jamis currently have 650b bikes and I suspect it may be cheaper at this point to buy a complete 650b bicycle than to build one. I did some research on this but I don't remember everything I saw.

I'm too lazy to check but I think the ISO for 26 inch, 650b and 700c wheels are 559, 584 and 622.

I think the frame geometry would need to be made for the 650b for it to be "ideal".

Yes, some people say 650b wheels allow you to have the speed of the 700c wheels without having the sluggishness of the 700c wheels in corners while. So, this implies 26 inch wheels would be slower. They also say it's easier to roll over grass, roots, rocks etc. with 700c. So, 650b would likely be easier to roll than 26 inch as well. I can certainly see your interest. But, if larger wheels are faster and roll easier on grass, snow, I'm leaning now towards 29ers or large-tire hybrids or touring bikes (like the Nashbar touring frame allows even 700x45mm tires, I tried it). Besides, I could not find Michelin Tracker and Continental TourRide tires in 700x2.2 inch. Since I'd prefer semi-slicks (not slicks like Fat Franks), that means 29ers would be out of the picture leaving only a touring bike with a frame from Nashbar and/or larger tire hybrids. I now believe I might end up with a touring bike with rigid forks and maybe later a city/rain/winter hybrid bike with suspension forks and studded tires (at least in the winter). Bike24 and Bikexperts in Germany have trekking (flatbar touring) frames.