The 5770 is the best value for money..........
That build looks good..........A Phenom II or i5 system will be better than a i3 though and specially as you want to run FSX

I also want to run Dirt 2. Does this spec seem ok for it?
An E5300 with 2Gb, HD 3650 plays it with ease.........
..........on the lowest settings.
So what is your question be more specific and for god sack your paying £212 for a mainstream GFX card i would want a lot of money back if that didn't play any game at mid (if not higher) settings ever made.
I'm really sorry if my newbie questions upset you! I wouldn't ask if I already know the answers.