I don't own a 85 jack, but have the forum knife instead. First some comparison pics. Sorry about the lighting, it's the middle of the night here

Top: 85
Middle: 76
Bottom: 66
Let's see. Some of these points are personal preference, but nevertheless I hope it helps to make up your mind.
It is just slightly larger than the 76, which is marginally larger than the 66. The blade length of the 85 and 76 is about the same.
It's definitely the heaviest of them all with its wider frame and feels like the bulkiest of the three (although the 76 is just as wide at its widest point). However it is still very pocket friendly with the nice rounded shape. The 66 feels quite a bit smaller (in pocket and hand).
Not all the 85s have the pen in front of the main blade, which I prefer. There's obviously the EO option if that is what you want, and there's a choice between clip and spear blade.
It is really comvortable in hand when using the main blade, the EO notch is just in the right position for the ring finger, I'd say it's like the 76 comfort wise. The 66 has a rounder handle and feels much smaller in hand.
The forum knife doesn't have a pen blade, but I imagine that wouldn't be as comfortable as the 76/66, because the wide spear blade stands proud and cuts into the ring finger (especially with the swedge and EO notch). Less of a problem with the clip blade I guess.
All in all, I'd imagine the 85 with a clip is very comparable to the 76. My favourite is the 76, but I doubt that's any help
