Well, the one thing a like about the Megolodon is it offloads to a soundcard if one is present. If that includes Pro Logic processing, that really jumps the headset up a notch, as the G35 lacks any way to upmix audio.
Remember, aside from the Megolodon, USB headsets ignore the presence of a soundcard. If you plug a USB headset, it becomes the output device, and handles the audio process through its own driver, pre-empting any soundcard.
As I understand it (someone correct me if I'm wrong), the Megolodon offers modes for 2.0 or 7.1. The issue is 5.1 audio then ends up feeling more flat. Upmixing to 7.1 makes the most sense in that case, but I don't know how much the megolodon actually offloads...
I know the G35 simply uses Dolby Headphone to virtualize a 7.1 field, bu that only works if 8 channels are avaliable. And from the reviews I've seen, some games don't work right...
As a general rule, if you have a soundcard, USB headsets make almost no sense.