MAXIMUM GPU for an ASUS M5A97 mobo?

Solution
Whatever graphics card you can afford. It all depends on if your CPU is powerful enough, your PSU sufficient enough and if your case fits such graphics card. It is not determined by motherboard but by those aspects.
Alright so how about these specs?

AMD FX-8320
GTA 980Ti
ASUS M5A97
8GB Ram
600W

Is this build compatible? I'm not too sure if 600W is enough or it might be, what do you think?

 
I do not suggest such a graphics card as the CPU wouldn't be able to let the GTX 980 Ti 'Fully unleash'. There would be quite a bottleneck most of the time.

Also, with a graphics card as valuable as the GTX 980 Ti you want to have a top quality power supply to keep it performing at It's best. There are a lot of power supplies on the market but only a selection of them are good so you have to provide the brand and model name of the power supply:

Graphics card suggest for that CPU:
NVidia GTX 970