mobo max wattage

Solution
A motherboard isn't a component which draws power as so to speak, rather co-ordinates hardware across circuitry which require power. The Motherboard wont be a factor rather the GPU/CPU the main ones, which 750W is plenty of headroom for that given it's a quality power supply unit. Yes the motherboard takes in the power for the CPU, and supplies 75W out of the slots for GPU's, but that is not for the Motherboard.
A motherboard isn't a component which draws power as so to speak, rather co-ordinates hardware across circuitry which require power. The Motherboard wont be a factor rather the GPU/CPU the main ones, which 750W is plenty of headroom for that given it's a quality power supply unit. Yes the motherboard takes in the power for the CPU, and supplies 75W out of the slots for GPU's, but that is not for the Motherboard.
 
Solution
Mobos do take power, they don't just connect stuff. The chipset takes power as well as any controllers for usb, sata, audio, etc. It doesn't take much but even hdds that are less than 10w are taken into account. It's usually around 50w for the mobo.

750w is more than enough. Depending on other components, you could do with just a 500w. The mobo doesn't have a max wattage pertaining to gpus as the majority of the power comes from the pcie power cables from the psu to the gpu.