I think it depends on the the guitar.
I find the 81 works well in
basswood guitars, and
mahogany guitars, where the added midrange responce of the 85 isn't required to fill out the tone of the guitar.
I put 2 85's into my (ALDER) Yamaha Pacifica a few years ago, and the results were spectacular. I never suspected such things were possible from the guitar.
However, the yamaha Pacifica whilst being a cheap well-made guitar is not an easy guitar to install to. I had to modify my scratchplate and install foam all over the damn thing to get rid of the noise, worth it though!