Fixed would mean less that 1024 most likely instead of 1280, there are still a few people who use 15" monitors.

I'm using a 19" 16:9 and it looks perfect in my opinion other than the post area being slightly overstretched.

I say keep it stretched as if it's fixed it would have to be over 1280 to make it look bearable on a wide-screen, however under 1024 for those who are on a budget.