GPU recommendations please

I have a NVidia GeForce GTS250 currently working in my PC. The downside is that I need to keep in-game AA and AF enabled because I never managed to pass AA and AF control over to the NVidia driver, even nHancer didn't help.I also tested with an ATI HD4870, with this adapter I was able to disable AA in FSX and use the driver's AA, but the adapter caused some nasty display glitches (which are known to exist in FSX for this GPU series; finding out that I'm not alone with this problem and it's a hardware/driver issue took me a reasonable amount of investigation), this made reading my LDS 767 displays a disappointing experience, so I switched back to the GTS250.I now think about changing my graphics adapter once more and use a newer model with GPU types different to the ones built on the above mentioned boards. And, I think of switching to Windows 7 x64 - I'm still on Vista x64.The questions for me now are:a) Will I be finally able to use the driver's AA and AF (which maybe give me better results than in-game AA and AF) when choosing e.g. an ATI HD5770 or an NVidia GTX260?b) Will I still encounter display anomalies with e.g. an ATI HD5770?c) Is it a wise choice to upgrade or are the benefits neglectible? Will I see a noticeable difference to what I have in either graphics quality or speed in FSX (i.e. +1 FPS or up, or more fluent graphics with less stutters)?d) If upgrading is recommended, what adapter would be the better choice regardless of the price it costs?The processor chips of both an ATI HD5770 and an NVidia GTX260 are different to those of my GTS250 and HD4870, so there's hope for me that the behaviour of these adapters differs as well. Maybe Windows 7 adds to improving of what I currently have in FSX...Andreas