PCIE 2.0, 16x vs 8x

I have a friend who is getting rid of his GT 240 for a new card and said he'd sell it to me for $20. I have an HD 7850 running on a pice 2.0 x16 slot, but I also have a second slot which would cause them both to run at x8.

Physx is something I've never really cared about, but I was hoping if I ran a Hybrid Physx setup it would improve my performance in Planetside 2 by off loading the game physics onto the GT 240.

My questions are, i) would/could it theoretically imrpove performance in Planetside 2?
ii) would running at x8 be a detriment to the primary card (my 7850)?

My CPU is a Phenom 6 1090t bumped to 3.4ghz

Thanks.

Thanks for that link! I think I'll do that with my GTX 260, use my Radeon as the primary graphics card, and use the GTX 260 as the PhysX card.

Sorry to hijack the thread, carry on OP.