What kind of fps are you getting now? The impact to MMO play would be minimal (in my best guess). Which one are you playing? Not sure about the racing games. FPS is probably be most sensitive to the performance hit.
I think either A or B would work. The wider FOV of the 3x1440x900 will provide a bit of a performance hit over 3x1280x1024.
Here is some info on bechmarking TH2Go -
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Most people find the stretching isn't bad. You may even look at 3x1680x1050. I found that in a 19" widescreen from Asus -
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1 - Vista not required
2 - I don't know of anyone who has upgraded from 3xNormal to 3xWS. I'm about to do it, once my monitors come in.
3 - I would say it isn't worth it. People report a noticeable performance hit over TH2Go. There is also less support, and fewer people here who can support you.
3 - Make the best investment in monitors that you can. It's not a component that you will swap out regularly. Procs and GFX have a much shorter life span. An investment there, doesn't have the same ROI.