Simply, a motherboard doesn't effect gaming performance, as they all should have a PCI-E X16 2.0/3.0 GPU slot.
Only advantages are, as you listed on is SLI/Xfire.
More you spend, you'll generally get better muti-GPU support, with SLI/Xfire running in X16/X8 or X8/X8 (same as first), with triple SLI/Tri-Fire, X8/X8/X8, X16/X16/X8 or cheaper boards with X16/X16/X4 or X8/X8/X8 and Quad SLI/Quad Fire with; X16/X16/X8/X8, X8/X8/X4/X4 ect..
But with motherboard there are chipsets also, better the chipset the better OC capabilities of your CPU, curruntly with intel 4th gen LGA 1150 CPU's you get this selection of boards; H81/B85/H87/Z87, Z87 is the only one that has a truely 'unlocked' capability for the CPU as if you have a "k" processor in a H87 board, you'll only get a limited OC whereas Z87, you'll get a full 'unlock' on OC.
Also, the more you spend the more features, i.e. USB, SATA (to a certain point), and supplier on-board features.
not only the number of pci ex,
-some gaming boards will have dedicated network cards to offload cpu usage compared to standard realtek network that's usually found on budget/normal boards
-overclocking features, better cooling for components soldered on the motherboard
-positioning components, leaving more space around the cpu, spacing the pci ex slots in such a way to allow you more spacing between 2 graphics, and spacing between the cpu socket and the ram modules
-there's also general build quality to consider. unlike desktop normal boards that sit idle most of the time, the components on a gaming oriented board will work at full or close to full speed for longer periods of time.
edit: some come in various colors to look better in transparent cases
Thanks! So basically no overclocking or sli, which suits me fine. Are there real differences in Asus H87M-E or h81m? Its close to 50-60$ more in my country, is the any advantages except number of ports?
Oh and are there any limitations as for GPU? e.g Gtx 750, R7 260x, 265, R9270?