I run BP6ES's also, but my ignition is Crane(actually Allison before Crane bought them) blue coil and MSD-6. I started at .035, tightened them up to .032, then .028, opened up to .038 and am back at .035. I've had the same plugs in for better than 10K miles(don't drive the 6 much lately, gotta get the seats in it).
So, experience with high performance ignition leads me to believe that you can go .035 no problem. The combustion chamber shape is different than a TR3.