I'm just trying to stay ahead of the curve and since we already have,
26"/559mm ISO
27.5"/584mm ISO
29"/622mm ISO

It seemed like it was time to try and get ahead of next year's big new wheel size.

700A will get you a monster wheel 22mm bigger than a 29er, the roll over should be fantastic and might be able to make some inroads with those that really want to ride a full rigid over stairs, but don't want to go all the way to a 36er.

650A comes in with a ISO of 597mm so for those that need a Goldilocks size between the 27.5 and the 29er this might fit the bill. Seems to be a lot of 29er vs 27.5 debate around here and 650A may just be the solution.

I think the 700A will have better rollover but the 650A will be more flickable and will corner better. I'm really not sure which one would be faster...

Oh and another consideration, 650A has a British standard size of 26 X 1 3/8", 700A is 28 x 1 3/8" So which one flows off the tong better when "er" is added to the end may be a consideration as well.