Its hard to say, in my experience dumbells work stabilizer muscles a lot more. If my bench is slacking due to factors other than chest strength I will switch to dumbells for a while. Ill wait to see improvement there before switching back.
I would say do your warm up. then add weight each set listening to your body. That is how you can find where you are at. There are a lot of factors that come into play since it is a compound lift.
To answer your question to the best of my ability i would say a bit more than double. 85 x 2 = 170. I would say 185 would not be out of the question. But everyone is different. Let us know how it goes, and good luck!