I doubt you will see much if any performance gain with that 580 either. Trainz primarily uses the CPU to do most of the work anyway.
If that is the case then why is it that i can put 2 Nvidia gtx 9800 cards in my computer and it will not run the route to a great extent ,if its only using the cpu it shouldn't make any difference ,then i put 2 ati 5970 in the computer and it runs far better near flawless ,so it does use the GPU'S on the video cards as well.
however for some reason [ driver related i believe ] nvidia seems to run Trainz better for me , and in SLI also ,people may believe that sli or crossfire make no difference, turn one of the cards off on a big route and you will soon turn it back on
with crossfire it only helps slightly with the right drivers.
if this is true that Trainz only basicly uses the CPU to run the game then there is something that Auran should be looking at and fix it fast
just my opinion
are all sim games run by CPU like trainz
regards steve