81 has slightly scooped mids, is tighter, more articulate, and more percussive. Its also the pickup most people have in mind when referring to the EMG sound being sterile.
The 85 has a (lower) mid spike, its thicker, chewier, rounder, and a little more forgiving. Its also a little more natural sounding than the 81.
IMO the 85 is mistakenly thought of as a neck pickup (I blame Zakk), when in fact its a very good and underrated bridge pickup.
I had an 81 in bridge & 85 in the neck of several LP's. I was always trying to tame the treble.....the 81 was the problem. I is/was a lot more trebley than I realized. I later got a pair of duncan distortions and thought, "wow, I should have made this move a long time ago".....looking back I had them backwards. I'll never put an 81 in the bridge ever again. 85 possibly (I also have an 89 -an 85 with the spilt tap coil option) in the bridge. Now a days i find my self moving in the other direction....lower gain pickups, they make up for it in TONE.....I let the amp work a little more now...........
89 -an 85 with the spilt tap coil option