I finished my 490 today. I can't say for sure the gains over stock since when I timed it stock I didn't know ash cuts fastest at very low rpm (lots of pressure). I can say I got nearly 25% faster cut than a muffler mod which was already 15-23% faster than stock. I tested later (not in this video) with an 8t rim and lower depth gauges, but no gains. It runs easier and faster in its peak power range with the 8t, but that's too fast for cutting ash. Once again it is an issue of setting up the chain for the power band and wood vs for practical all around work. I didn't fill the bottom of the intake port, so it has a bit of extra power higher up unlike my 590 which is never ending low end torque; smooth wide power band.
Sucks that I used some green permatex gasket maker to seal the transfer covers just to find it melts and blows out. It still ran well for the test cuts so far. Looks like I'll have to tear it down again and do it right with some 1184