8) Unless you have the $ for a 8800 Ultra...
The
GeForce 8800 GT(new) card is for you...with better and cooler performance than the 8800 GTS...
You can get a 400 watt power supply for about $60.00, I got a 1000wt power supply thinking of two cards, but only have one PCIe slot! So much for overpower and capability.
With your config, you should be able to use two of whatever, however my single 8800 GT card rules!
TRS2006, runs like a TV!
Initially, instead of nVidia developing a new 9800 series (though they now have announced a 9600 GT) they instead started simply improving the 8800 series. First was the 8800 GT, which upon release, was indeed as fast if not faster than the first release G80 core 8800 GTS 640MB and 320MB. Later Nvidia changed the 8800 GTS with an unlocked 112 shader processors (which was faster than the original 8800 GTS). However, with the GT being more powerful than it's big brother, the 8800 GTS, nVidia has released a NEW version of the 8800 GTS (based off of a new G92 core and sporting 512MB VRAM). Unlike the previous G80 based 8800 GTS, the new GTS has lower power requirements BUT is still more powerful (in fact it rivals the 8800 GTX).
So in short the 8800 GT does have less power than the 8800 GTS 512MB. Here's some links with the new variants.
8800 GTS (G92) 512MB vs 8800 GT
http://www.gpureview.com/show_cards.php?card1=548&card2=544
8800 GTS (112) (G80) vs 8800 GT
http://www.gpureview.com/show_cards.php?card1=545&card2=544
8800 GTS (96) (G80) vs 8800 GT
http://www.gpureview.com/show_cards.php?card1=475&card2=544
Really when you check out the stats, the 8800 Ultra is nothing more than a rather expensive, overclocked 8800 GTX (and in the area of $700 - $800 USD)
It's actually much cheaper to buy certain factory overclocked 8800 GTX's.
Just as a comparison
BFG 8800 Ultra 768MB:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143107
BFG 8800 GTX 768MB:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143093
BFG 8800 GTS 512MB:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814143119
In comparing the specs there is almost no difference in GPU or memory speed (a few mhz but nothing substantial, or that would give a huge increase in speed, and certainly not $200 USD worth of speed). And just between the 3 listed, it looks like the 8800 GTS 512MB (G92) could give the 8800 Ultra a run for it's money.
EDIT: Doh! I should appologize, I didn't even consider the fact you might be on a budget, sorry if I came across as pushing some of these cards. The 8800 GT is a fine card, plenty of power, even for Trainz. But again Trainz won't take advantage of SLI. The twin card setup MIGHT (note MIGHT) retain higher frame rates but there is a very low chance of that.