I keep coming back to this, and I think I'm just going to try it.
Near as I can tell, lean burns faster than rich (I've heard some conflicting info).
I know that part throttle burns slower than WOT. This is what vacuum advance is used for in cars. Based on that, I know I can get away with more timing advance at partial throttle. I would gain some MPGs. The danger is at WOT.
I know people have stated the bike runs lean from the factory. It probably also uses conservative timing to account for bad gas. I plan to first richen up the AFR through a larger main jet. The chart shown here
indicates the main jet covers 3/4 to WOT. If I can get it rich enough, it should tolerate more advanced timing at WOT as well. All in all, more MPG and more acceleration. I'm running no mufflers, and I'm doing the ear shave. I'm planning on a 138 main jet, based on that post. I'll probably buy a set of 140s too, just to try.
The chart in the service manual (page 15-7) shows a range of timings. I'm assuming that's the tolerance band. At 1100 RPM, it shows ~3.5-7 and at 3500 RPM it shows ~24-27. That tells me that without any other modifications, I should be safe to push the 1100 advance to 7 degrees. I'd use a timing light to verify the timing of each coil. With a rich WOT mixture, I MIGHT be able to push 8 or 9 degrees.