I think it performs fine. With focuses sight it is still a very formidable tank hunter.
Sorry, but no.
First of all you rarely want to be using focused sight because of the massive mobility penalty.
Secondly the SU85 desperately needs a higher penetration OR higher accuracy. It fails to penetrate both the Tiger and Panther reliably enough to make it worth the cost. It is 100% worthless against infantry (at least the Panther has MGs and speed to crush) - at 12 pop/tank if you build more than one (which you'll have to do) you'll really struggle to achieve any reasonable level of AI ability - especially when you start having to deal with Vet 3+ Obers or Vet 5 Volks... good luck.
I could keep going but I don't want this post to end up being too long. Basically you're paying way too much for a tank that can't reliably counter anything that you actually need it to counter. It has an effectively negative impact on your ability to counter Axis infantry (which get crazy scary late game). Not to mention the fact that PaK40s just rip the SU85 a new one. It is pretty much relegated to countering P4s/Ostwinds, and doesn't even do that well with PaK40s on the field.
It could use some combination (but not all) of: increased pen, increased accuracy, increased mobility, +5 range, +hp, cost reduction, and/or pop-cap reduction. I'd honestly build Su76s over Su85s in 90% of situations and the Su76 sucks too...