Having owned and ridden both (evo 2 first, got nicked, then 45650b, cracked). I can comment pretty well on both.
I don’t know about mixing wheel sizes but two things:
The 45650b has a high BB, so switching to 26″ wheels might well work.
But the 45650b has the ‘gas pipe’ connection between the seatstays and the seat tube. The evo 2 has the much more slender four-piece seatstay arrangement so is more compliant. I can hear the naysayers out there, but I really did find the evo frame more springy and soft than the 45650b.
It’s a tricky one. I loved the ride of the evo, but it was limited by the straight head tube and wheel size. The 45650b is more up to date with standards, but the frame itself is just not quite as nice to ride.