There's no question that DDR is the way to go. While ATI has some seriously superior approaches to handling the problem of limited bandwidth (on chip, in hardware), the SDR cards are weaker performers with current drivers & current software.
Also, the comments above are right on about the memory being the hindrance with o/c-ing the card. The cooling fan on the retail Radeon cards is pretty much cosmetic--the heatsink will do as well. The Radeon isn't a super-hot chip (like some competitors chips, which will incinerate themselves given the chance). Putting extra cooling on your chip really won't help you much anyway, since with the Radeon you'll have to do sync'd o/c-ing. The chip & memory need to be o/c'd together, at or near the same frequency. The card gets unstable pretty fast if you push the chip and memory too far from each other.
I run my retail 32DDR at 183/183, and have no problems at all. I've not tried any higher, and probably won't. Testing results posted on the Rage3d Radeon forums seem to indicate that once you hit 185 you've gotten most of what you can get from the chip. A particular forum member o/c'd his 64DDR card, if I am remember correctly, to 215/215 successfully--but he only got 10 more points from 3dMark than he'd gotten at 183/183 (retail 64DDR default). With such meager o/c performance gains it's just not worth the risk, IMO.