hmm, possibly 9550 SE, I don't suppose you could squeeze out for the 9600SE could you? because I believe those are supposed to be able to OC to PRO speeds, of course that might have just been the 9800SE's come to think of it..hmmm...that's kind of a toughy. The LE and SE editions usually suck balls so if you were to just get the generic 5500 that should be good. but I believe the generic FX 5700 is only $100 now, what's your graphic cards budget?
I think I'm going to have to saaaaay FX 5500 although generally previous gen ATI cards beat out nvidia, but I'm thinking that perhaps since that 5500 isn't LE like the 5700 it'll perform better than the 9550SE.
BTW I suggest you get the 35w 2400+ XP-M for OC'ing, I too was thinking the 2500+ XP, but man I got this chip up to 2.3GHz 38C Full load and I haven't even begun to try and push it, I just wanted 200FSB so I could run my pc3200 RAM at it's designed speed