Please don't go with XFX. The noise/temps on their Double D coolers are pretty bad. I can link you a couple of reviews from decent places, but I've also owned one personally (7950 DD Edition), and I'm not exaggerating when I say it was the worst graphics card experience I have had, and had to sell it on within a month.
Review 1:
http://www.anandtech.com/show/5476/amd-radeon-7950-review/17 (most of XFXs 7950s are just binned 7970s. The cooler is exactly the same)
Review 2:
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/51347-xfx-hd-7970-3gb-black-edition-double-dissipation-review-12.html (the fact the temps are worse under load than stock is a real turn off)
Review 3:
http://www.anandtech.com/show/5314/xfxs-radeon-hd-7970-black-edition-double-dissipation-the-first-semicustom-7970/2
Some reviews are very positive about it though (which I find a bit confusing) claiming it's the 'quietest card they've tested' and what not. Maybe I just had a bad sample, but the multiple forum posts I read about the XFXs "bad noise under load" and mediocre temps, as well as the three reviews above, convinced me that the card was just not that great.
The problem I think stems from the fact that it was the first aftermarket 7970 to be released, and hence (in their rush to release reviews) could only really be compared to the stock 7970 (which of course isn't and shouldn't be any sort of contest). A couple of reviews say stuff like the card had "done well with temperature reductions of 3C under load"... I mean c'mon, no aftermarket card should be that close to stock performance, esp. when it's a 2 fan model.
The ASUS coolers on the other hand are very highly regarded in my opinion. Personally I think the best 7970s out there are the Gigabyte ones, but they don't have the same looks as ASUS/XFX it's true. The one thing I don't like about the ASUS 79xx is that they are triple slot, which is one of the reasons I ended up going with an ASUS GTX 670 in the end.
EDIT: Also you say your PC is currently silent, mine is currently as well. With the XFX 7950 people were complaining of the noise on Skype,
during League of Legends which is hardly the most demanding game, and should be EASILY handled by the 7950.
M