Here's my WC68/B2650 combo in action last spring.
And it can chip green (not cured) aspen up to 6" diameter if you slow the feed speed adjustment to a crawl.
The feed roller speed adjustment is quite touchy at slow feed speeds - I've gotten used to it but have thought a hydraulic flow or pressure reduction of some kind for the feed roller motor flow control valve would better the speed control's usable range and make slower feed speeds way more finely adjustable.
It's only been used in the bottom quarter of adjustment range al along, and with our lower pto hp machines that's where it's needed.
That's the only "complaint" I have with this unit.
Still sharp and cutting like new after 2 winters and probably 20-30 yards of chips in all put through it.
For the shipped price of this unit 2 summers ago, around $3500 all in, plus a 5 gal jug of 32 weight hydraulic oil, I'm VERY glad I got it!