I had trouble getting B-miner to work, luckily gminer works fine. Current settings, core +240, memmory +360 80% power limit, rate of 0.65 graphs/min. I use Inno3D TunIT for changing settings since I have an Inno3D videocard, but you can also use Afterburner from MSI which is more popular.
Edit:
Optimum appears to be core +130-135, memory +550-600, power 100% for my Inno3D RTX 2080 Ti, on average I get something like 0.75 graphs/s.