GoTo surfing vs True Surfing
I can almost guarantee most of the APS difference is due to movement, as opposed to gun. But I'm not at all convinced it's as simple as GoTo vs True Surfing. I think DrussGT could probably be just as strong with a True Surfing algorithm. I also think it would take me a while to get a GoTo algo to perform as well as my True Surfing, and vice versa for Skilgannon. It has been in the back of my mind for years, though... Maybe I'll try GoTo eventually?
Most likely, I think it's a bunch of smaller things - maybe better bullet power selection, better tuned surf stats, more effective surfing algorithm, better handling of a few special cases (like anti-ram), less (or less harmful =)) bugs. DrussGT is just badass. =)
PS - Also actively developing here, but no reason to release until I have enough to show for it.