Just buy a card that you can afford and need that will play most of your games at the settings you want... You may not need to turn on MSAA.
Also, you are going to keep your monitor for 3 years are more, while you may upgrade your card every few months or a year - so even if the card you can afford can run everything at max settings is not available now, maybe in the future years when the price drops or better pricing higher performance cards come out -or you can always add a second card later for SLI/Crossfire... these are always your option.
Just for your reference - I run a GTX 670 on 2560x1440 monitors all day gaming with max resolutions (no MSAA) and stress testing, happy with the performance so far