The thing with SLI is, it really shows its color at a higher resolution. So I'd probably say 1680x1050 or 1920x1200.
I believe 1680x1050 run around $250-400 and 1920x1200 run around $700-900.. I might be off a bit.
1920x1200 is to much for a single X1950XT, it will really lower performance at that resolution.
I think 1680x1050 is the best purchase for you. 20" or 22" depending on how much you wanted to spend on it. Samsung is a really good brand.
As Jackz50 said,
http://www.newegg.com/Product/Produc...82E16824001095 this is a pretty good LCD. You won't notice ghosting at all and its widescreen and supports 1680x1050. (Sorry I don't have any UK Links)
The pricetag isn't much more than a 22" flatscreen CRT would cost either.
On a side note, the current 8800GTX and 8800 Ultras run "True" DX10 games fine. I've seen Crysis played on a G80 and it runs fine on Ultra High (Sorry I can't say anything more..
), and i've played World in Conflict DX10 and it runs fine on max (40-120FPS, and this is Beta). The reason why most people think the G80s cannot handle DX10 is because all the current DX10 games are patched and they were designed for DX9. Its basically a cheap port and it ruins the performance.