Quadro FX 1800 vs Quadro FX 4600 for hybrid physx

[Guest]

Hi, my rig is

Intel core i5 2500k @ stock speed
Ati Radeon 5870x2 1gb vram Crossfired
16gb ddr3 ram
Biostar TZ77XE3 motherboard
1050W psu
Windows 7 64 bit ultimate

So I can get these two cards for free, so I was wondering, which one would be better for a hybrid physx solution for games like Borderlands 2?

 

[popatim]

I would go with the 4600.

 

[Guest]

Nevermind, it turns out my case doesn't have enough room for another dual slot card. I'll have to settle with a 1800 or 3700 or 3800.