I still like the price of the corsair, although those TwinMOS' arent THAT much higher. (I can always wait a bit longer, I guess) I know four people that have XMS Pro, and they havent had any trouble with 'em. One of them is a heavy OC'er, I might add.
Well you're comparing $69 for 512mb of Corsair against 1gb of Twinmos for $87, can't beat that with a stick
Also no, you don't need heatspreaders...assuming you are infact going to OC them "mind you you will need voltage! I cant stress this enough on this chips"
2.9-3v the TwinMOS will easily take and that should allow you to hit 220 with 2.5-3-3-7 timings.
Also Diablo hit the nail on the head, good RAM is basically only for OC'ing, other than that the price isn't worth it if you're simply going to run them at stock unless you really just want to brag.
Also if you're pumping 2.9-3v through them sticks it might be a good idea simply to have an 80mm fan hovering a couple inches above the RAM modules, this will simply ensure they stay cool.....in some instances the heatspreaders can actually be worse because it's really crappy thermal tape on the inside that's trying to move heat away and they don't work very well.