My new gaming rig

Whats the resolution of your 17" monitor? A 4850 can run everything on high on my 19" at 1280x1024, if your 17" is only running 1024x768 then a 4670 would be able to run it on high and a 4850 would easily max stuff out, no need for a 4870. What PSU do you currently have? What case too as even the 4850 is a fairly long card and all modern GPUs need a case with decent airflow.

In that case a 4870 will let you play on max, however, since you picked an SLI board and an ATI card one of those needs to get changed. This board from ASRock will let you crossfire a second one down the line
http://www.newegg.com/Product/Prod [...] 6813157164

That PSU needs to go though, especially if you intend to CF down the line, it doesnt provide nearly as much as it would like you to believe, its limited to 47.5A on the 12 volt rails. If you intend to crossfire down the line a 750 watt PSU is needed, the TP-750 Blue from antec is modular and provides plenty of power for 2 4870s
http://www.newegg.com/Product/Prod [...] 6817371022
if you dont intend to crossfire you can drop down to a good 500-550 watt PSU