Question: I have an i5 760 system with 2-way SLI capable mobo with a GTS 450 1Gb DDR5 128 bit VGA, I'm still running a single card right now but I'm planning to scale up soon but first I would like to know:

1. Is it better to SLI 2 cards or just have 2 VGA card one as a primary and a seperate one as a dedicated physx card?
2. Is it OK if I use two GTS 450's from two different manufacturer as a SLI tandem?
3. Will there be any conflict if one of my two VGA cards in SLI has OC and the other one don't have OC?
4. For example: is it OK if I use a GTS 450 1Gb DDR5 128 bit from a manufacturer A and a GTS 450 1Gb DDR5 192 bit from manufacturer B as an SLI?
5. Does the example in question No. 4 will work for primary and physx card set up too?

Answer: 
1. SLI will be better than 1 VGA and 1 for physX. Unless you specifically play a *bunch* of physX games and a weak CPU, you'll find a better benefit to having the additional rendering power.
2. Yes.
3. Faster card will downclock to the speed of the slower card. It will effectively run without the OC.
4. I don't know about memory bandwidth differences; I think that should work, since they are both the same size memory. If they are not the same size memory, then the card with extra memory has the extra memory disabled in SLI.
5. Yes, it'll work fine.
1 It *depends*... Darth reason, difference between main and PhysX card also play game (as I see in my config)

...

4 Yes, but bandwidth will be lowered to thin card bus

5 Yes, but use 128bit card as PhysX and 192bit as main for better results