Decent Graphics Card for my Setup

[BadWhippet]

Take care when upgrading a graphics card that what you are buying IS significantly better than what you already have. As reference, I always look to Tom's Hardware Hierarchy Chart (see the table part way down the page). This ranks nVidia, AMD and Intel chipsets side by side in performance (benchmarked) order. Note: an upgrade that is less than three levels is not much of an upgrade and is not recommended. Also, bear in mind memory on your existing card. If your old card has 3Gb of on-board memory, but your shiny new card has, say, only 1.5Gb, this will dampen the performance increase you would expect to see considerably more.

I know very little about AMD (I use nVidia) but regarding nVidia's numbering, only the last two digits refer to performance (the first is just chipset family). Any card that is 40 or less (540, 640 etc) is not a gaming card and should be avoided if you want the best out of 3D intensive games such as Train Simulator. Example: a 640 is FAR worse than a 580 (still a top-grade performer) - and a big mistake as an 'upgrade'. People sometimes fall into that trap and end up with a card that is useless for games.

[asfinmja]

regarding nVidia's numbering, only the last two digits refer to performance (the first is just chipset family).

And even this is not true anymore, as GTX 780 has GK110 (same as Titan). But GTX 770 and GTX 760 have GK104. Basically they are faster (higher clock rates) and cheaper (at least originally) versions of GTX 680 and GTX 670.