as promised earlier, here's my experience:
At last something that is more or less up to date ... :P So, I'm certainly happy to have taken the chance of getting another stick. the machine works noticeably faster (supposedly double data rate should be giving like 5% more perfomance when doing office stuff, but I think it's more for me). No instability issues so far, but the next big test will be the coming up Call of Duty 4 release, then we'll see.
But anyways - just stating the obvious - more is better, especially if you can get it just like that ;)