I like my 6800GS a lot -- it is the best performance for its price (about $200).
The 7800GS is higher performance. Eagl was saying he likes the 7800GS, I believe.
A factory-overclocked 6800GS is about $200. The 7800GS is about $300. (For XFX brand from Newegg.com, anyway.)
However, I don't think these cards will be silent. The 6800GS I have is definitely noisy. If you want silent, I'm not sure what to suggest of any of the newer, higher-performance cards, as they all dissipate lots of heat and need substantial fans.
If you do want to minimize fan noise, here is a suggestion:
http://www.electraforge.com/brooke/misc/riva_tuner/riva_tuner.htmlOr you could buy a lower-performance card that is still fine for Aces High Maybe a standard 6800, not a 6800GS, for example -- I have a 6800 in my machine at work, and it is much quiter than my 6800GS. Of course, it is lower performance, too.
Maybe someone has experience with the newer Radeon cards and can comment on their noise.
Some card reviews mention the card's noise output in db, too. If you search on the GPU (such as "6800") and the word "review", you'll find all the usual sites.