This is kinda tough to answer, as you are about the same size I am. Essentially, you are in between sized for bikes right now... much like I am in the process of trying to upgrade to a CR 125.
I have run out of room on my CR 80 Expert (same size as the yz 85). You would run out of room on a YZ 85 as well, and grow out of it very quickly.
It depends on how much track riding you do compared to the trail riding you do. If you're doing tight turns and very technical stuff, then it's not going to be a good bike for you. If they are more open trails with very few obstacles, then it might be good for the short while that you will still be small enough to ride it...