When I used my 275 with my X5's I had it at around 85 but it's all a matter of taste and how you like your speakers to sound. I run all tubes so I dont need to drop the bias too low to get "tubey" sound. I run tube DAC, Don Sachs tube pre, and tube amps. One thing on the 275, change out those stock signal tubes to some NOS. The stock tubes just don't make it. It brings that very fine amp to another level.