FX Quadro 4800 or 2x4600 (SLI)?

Hello again, Forum!

Since you guys never give me reason not to ask, here I am again, looking for suggestions.

The gist of it is : a friend of mine is sick of rendering his 3dMAX scenes with his Phenom II (1055) so he's looking into the GPU alternatives. he's been looking around the shops and we're discussing if it's better to get a single FX Quadro 4800 (for about $350) or two 4600's ($300 for both) for an SLI setup.

Obviously the main goal is performance and cutting rendering times, and if it can happen for relatively cheap - that's an added bonus. gaming isn't even on the list.

current hardware:

MB- ASRock 770 Extreme 3

CPU- AMD Phenom II (X6)

and 4 GB RAM (i think, might be 8) 

PSU is at least 800W

 

I'd be happy if anyone can give his/her opinion on the matter, and suggestions are always welcome!

my guess is whatever gets you the most cuda cores / dollar