mhm, either, now for my actual advice, I'd get 1 gig for single channel right now, save the money you would use on the other 512 MB stick and wait till you can get another, than you can have dual channel 2 gigs. and Yes I know you have a 939, just makes more sense that way, and for the money you'd pay for 3 x 512 MB high end ram, you can just get 2( 2 x 1 gig dual) or 3(single channel) gigs of Kingston or Cosair, or Mushkin value ram, really.. you'll get better performance from 2 gigs of value ram than 1.5 high end ram, plus it will cost you alot less.
duh me, I just read the fact that you have a 754, but this is still true : you'll get better performance from 2 gigs of value ram than 1.5 high end ram, plus it will cost you alot less.
You won't even notice the better timings if you not oc'ing.. and really with ram.. its a so slight gain, not worth the money at alll.