Dilemma: 285SLi vs 295+PPU

Hey,

I'm using an Asus P6T Deluxe V2 board. My initial plan was, to use 2 GTX285 cards in SLI. I then got to reading about dedicated PhysX cards etc., and seeing as I have a 9800GTX+ lying around, I figured that it would be really cool doing the 2 GTX285 AND the 9800GTX+ as PhysX card.

However, this proved to be impossible with the layout of my Asus motherboard, and so I started looking around for either a PCI-E x4 card to use for PhysX, or a PCI card, as I came across a thread.

A guy says, that the probably best thing to do is just using any proper PhysX card with a good graphics card, and save some money instead of using SLI.

So, I'll ask you guys:

I assume that the 285SLI setup will be better than the 295+PPU, but how much? There's a considerable amount of money to be saved.
Also, will using the 9800GTX+ as a PPU limit the 295 in any way? I saw someone saying that it would bring down the better card to the lesser card's clock speeds.

I hope someone can enlighten me a bit on this

Thanks in advance,

Ottosen.

*double post mistake

Yes, surely, but would dedicating my 9800GTX+ or PhysX not give an even better performance? I mean, it's just gonna lie dormant anyway