SLI, Crossfire motherboard efficiency

[jimmi_payge]

So, I've been doing alot of research on motherboards for my first PC build. Where I'm confused is that most boards that are less than $300 have two PCI-E slots: one that's a 16x and the other that'd be for the SLI-Crossfired card, that's only an 8x. What is the difference in performance difference for running two cards in such a setup versus spending another $150 to upgrade the motherboard. Or would I just be better off investing that $125 in a better GPU?

 

[Ectomar]

Putting it into a better single card would probably be best

 

[Rockdpm]

Ok i would like to explain a bit on this, when you have a X16 slot and a X8 slot, the bandwidth in SLI/Crossfire is gonna be X8X8, when you have a X16 slot a X8 slot and a X8 slot. your gonna be a GPU Setup of x16 in the top card and the other two will be running in x8 mode. Bandwidth is shared. If you are doing a X16 and a X4, don't do it. As for Dual GPU cards, its still the same as SLI/Crossfire. the other GPU utilizes the bandwidth of the other PCI express slot.

 

[jimmi_payge]

Ok i would like to explain a bit on this, when you have a X16 slot and a X8 slot, the bandwidth in SLI/Crossfire is gonna be X8X8, when you have a X16 slot a X8 slot and a X8 slot. your gonna be a GPU Setup of x16 in the top card and the other two will be running in x8 mode. Bandwidth is shared. If you are doing a X16 and a X4, don't do it. As for Dual GPU cards, its still the same as SLI/Crossfire. the other GPU utilizes the bandwidth of the other PCI express slot.

I was aware that the x16 slot defaulted to x8 if you have the second card in an x8 slot, (I should've mentioned this). What I was asking is this: Would it benefit me to spend the money getting a motherboard with multiple x16 slots? What kind of difference in performance would there be?