I know there is no 700Mhz Pocket PC out.... yet.
There will be a new pocket pc available (ipaq) in october, that has a 700Mhz CPU with 512mb RAM.
About the size of the games.
I've heard that you can 'rip' your PSX games to sizes like 10, 20 MB.
I've tried this myself with a game called Soul Blade (fighting game).
It was around 500mb, when i ripped it it was around 30 or 40mb!
So the sizes of the games are pretty low, if you cut out the videos.
I did a search on google, and found a program called PSXmc that can RIP the movies (and a couple of sound files) out of your game.
I don't know how it works, but i've read that works

.
get the program (japanese site) or use direct link.
Please do understand that i am not supporting Warez stuff of any kind, offering a solution to play your PSX games on your PPC.
Thanks for listening again

.