Since it's DDR2, you aren't going to notice a difference between the two. If there's a significant difference in price, get the set that costs less.
Thanks for your answer. No there's no significant cost diff. The issue was i purchased 4 x 2GB PC2-5300 667MHz one of which proved defective so they want to replace it with a PC2-6400 CL6+ @800MHz. I am also going to buy 2 more PC2-5300 667MHz so i don't have a compatability problem with mismatched chips (bin there dun that lol) but what to do with the 6400 CL6 chip ? Maybe ask'em to up a pair 'em. Thanx again.