Flight simulator is one of those games that require lots of CPU power as oppose to GPU power. Purchasing a 800$ videocard isn't going to give much bang for the buck with this game. Take a look at this for example (link below), the difference isn't huge between GPUs.http://www.tomshardware.com/reviews/core-i5-gaming,2403-10.html
Look at this article for a good reference on which card you might want to buy that match your budget (link below).http://www.tomshardware.com/reviews/geforce-gtx-460-radeon-hd-5570-gaming,2697.html
Good luck with...training.