Welll.... There are a few schools of thought on this. My personal opinion is that one of the big advantages of AMD CPUs is that I can change the multiplier. So I don't use the latest and greatest ram and save a lot of money (and have more RAM in my PC) by just running at 166FSB with PC2700 (which is dirt cheap). I was comparing a 512mb stick of PC2700 from Samsung with a PC3200 stick from Corsair the other day, and corsair was 2.5x as much. I doubt the performance difference is more than 5-10% max, so it isnt worth the $$ to me.
The other school is that extremely high FSB is where it's at for the best performance. This is true, of course, as long as you can still set your ram to aggressive timings at that FSB. I remain unconvinced that it is a really noticable difference in day to day usage, however. Sure you get bigger 3dmarks and SiSoft Sandra memory scores, but can you really tell without using a benchmark?
Having said that, Bartons are moving to 200FSB apparently, and Intel chips don't let you change the multiplier so you have to have good ram. The PC3200 or PC3500 is somewhat more futureproof for this reason I guess. I never beleive any hardware is futureproof, though, so to me the bigger reason to pay the premium is for the chance to get some extreme overclock and really high benchmark scores.
The truth is probably somewhere in the middle. I would use super beefy ram if I had lots of disposable income, but I view it as an expense not worth my money with limited funds.
Some good reads:
http://www.overclockers.com/tips00324/
http://www.xbitlabs.com/articles/mem...ay/ddr400.html
I have never had a problem with RAM purchased at the same time from same vendor being incompatible, but you might wanna look around at amdmb.com and see what their comments are on this. My instinct would be to just buy 2 sticks without "compatibility testing" if they were cheaper.
Hope that helps a bit.