I can't talk about the Parhelia as I haven't seen one in action. I have read on Murcs forums about the banding probs though.
I run a G550, Which I think does a great job, but then... This system is for NLE. My daughter does use it for some mild gaming... Namely
GTA III
simms
Delta force II ( Net multiplayer).
To which end.... The G550 seems to do ... OK