well if you are looking at Corsair's XMS, go for the 3200 (DDR400) over the 2700 (DDR333). the XMS PC2700 uses 7.5ns micron chips. take a look at this PC2700 review @ OCPrices.com:
link
check out the page on XMS PC2700. the micron chips used on this memory are barely OCable, and i'm assuming that of you go with DDR333 over DDR400, you're going to want OC it a little bit (correct me if that's a bad assumption). anyways, since then, Corsair has started manufacturing XMS PC2700 w/ samsung chips instead, improving their OCability quite significantly. this is also in the article, but read through it carefully to get all this info, b/c the product name and revision # remains the same for both modules w/ micron and samsung chips. they only differ in product code, so make sure you know which code to go with if you insist on getting XMS PC2700. i would advise against it only for fear of getting a module w/ micron chips. if you are going to get DDR333, get Samsung original (samsung chips on samsung PCB). higher wuality and a much better OCer.
the XMS PC3200 is a different story. although i havent read any reviews on it, i would assume that under the heat spreaders lie samsung chips since it is rated to run @ 200MHz fsb (400MHz DDR). since we know that DDR400 isnt a JEDEC approved standard yet, all DDR400 memory makers are curently just hand-picking exceptional batches of DDR333 chips and OCing them successfully to 200MHz fsb and slapping a "DDR400" label on them. and according to the above reivew, all the modules able to OC to 200mhZ fsb or close to it are using samsung chips. so i would say its safe to get XMS PC3200 and not have to worry about certain components not being high quality. as for the XMS PC2700, you might have to worry about quality...
i'm going with Samsung Original PC2700 when i build my system w/ a SiS 648 board.