Size of tghe monitor has nothing to do with performance. A 55" HDTV will yield the EXACT same game performance as a 23" LCD. What matters is the resolution. If both panels have a resolution of 1920x1080 (1080P) they will perform the exact same with regards to frame rates and whatnot. What will be different is how the picture is presented on-screen. The larger the screen (resolution being equal) will look less sharp than a panel of smaller size and the same dimension due to the pixels being larger (look up "pixel pitch" online for reference).
2x monitors will have a bezel right through the middle of the screen and will look horrible. 3x Monitors will require more GPU power due to the increase in resolution. Also, for 3x Monitor support you will need another GTX 580. Latency will not be an issue with a Simulator due to the slower pace of the action. The only time latency is really that important is when you are playing a first person shooter. Unless you are looking at an LCD made 10 years ago the latency will not be an issue for a simulatore like TS2012, FS9, FSX, Prepar3d, etc.. etc..
The most important thing to look for in a panel is panel type (TN, MVA, or IPS), resolution, and screen size. The best looking will be a 30" IPS display, but it will also more than likely cost you more than $1000. IPS will have the best colors, best viewing angles, and highest cost. MVA will have good viewing angles, solid blacks, and poorer response times. TN will have the fastest response time but the worst viewing angles and color respresentation. However, TN will also be the cheapest. If you are looking for a large screen HDTV to game on, than look at LG and Panasonic. I do believe both of these panel manufacturers use IPS displays (watch out for a panel lottery though....sometimes manufacturers will have the same model of TV with different panel types).
I personally use a 30" Dell 3007WFP-HC and a 23" Acer H233H (Smaller panel for Netflix in my office). I love my 30" Dell but it runs at 2560x1600 which can stress my system depending on settings (4.2 GHZ with Evga GTX 480 SSC). I have used a 23" LCD, 30" LCD, 32" HDTV, 37" HDTV, 40" HDTV, and 52" HDTV as a computer monitor and the 30" has all them beat with regards to color, clarity, and sharpness. Anything more than 37", IMO, is just too big for a computer monitor. The highest resolution you will get on an HDTV is 1920x1080 and that is just way to low resolution for me at bigger than 32". At resolutiuons beyond 37" (even 37", to be completely honest), the picture just does not look very good to me. Some folks don't mind the loss in sharpness and clarity, but I just couldn't stand it.
Hope this helps. Let me know if you have any questions.
