Just about everything worthwhile runs on Slim PSPs now. They had homebrew up and running right from the start...the day the Slims came out in Japan, I hacked mine and had Neo-Geo and CPS2 running smoothly.
Here is the CPS/Neo-Geo author's home page, with the latest updates:
http://nj-emu.tfact.jp/If both an original and a slim are loading off memory sticks, would the slim still have faster loads because of the extra ram?
Doesn't seem like it, BUT the extra ram can be used to make applications run better. Take the Neo-Geo and CPS2 emulators, for example. On a phat PSP, you needed to make cahce files for every rom, effectively doubling the size of each game. The slim uses the extra memory to eliminate this...every CPS2 game can run on the ROM alone, and only a few Neo games need cache files now. The emulators also run even smoother with no hiccups.
I use my PSP slim all the time...it's easily my most-played system. Got an 8gb stick FILLED with stuff, and what's even better is that I can play it all on an HDTV too.