Welcome to TBN and thanks for your input.I can "almost" help you out. I have the 8" model of the Woodland Mills you're looking at. I'm a machinist by trade, and have done a lot of fabrication work too. The quality and thickness of materials of my WC88 are excellent. The hydraulic feed is a bit fussy, in that you breath on it and it goes from too fast to too slow. Once you fine the right spot, it does stay put. If you're just chipping fir boughs it will clog, as will most chippers. You need WOOD not just branches full of those fine needles. If I'm into a bunch of fir or hemlock boughs, I run through a few branches, then follow up with a good chunk of wood to clear out the needles. If you can swing the WC88, it does allow you to feed in a much bigger bunch of stuff than the 6" model. It's not that you're going to chip 8" firewood, but rather the bunching up of branches feeds better through a bigger chute. Hope this helps. The Woodland Mills unit we have is really a great attachment for our property. Wish I had one years ago! Keep the belts tight, don't chip dirty limbs and you should be fine.
I can certainly swing the WC88 but I am concerned that the belt drive system is just more potential problems down the road. My main concern is whether or not the WC68 will feed the small branches (with needles) better than the chipper I have now.
I guess there is no way to know unless I get personal experience with one. That comes at a cost.