Hi, Glenn, et. al.
My 685 is very similar, with the GTSIO-520K's. 3400RPM, 44.5 inches MP at takeoff to generate 435hp. Thankfully, I have not had as much difficulty with cylinders. I think it's because of my constant monitoring of CHT's via my EDM-800's. At any reasonable kind of altitude (thinner air, less effective at cooling), I cannot run with the cowl flaps anywhere near full closed and still keep the CHT's under 435 (I like to leave a margin for error below the 460 max) with a properly-leaned mixture. That generates about a 5kt airspeed loss due to the drag, but I'll take it vs. cooking the cylinders.
By the way... I rely heavily on the engine analyzers to show me the individual CHT's. The OEM gauge shows just one cylinder... and it's not the hottest one. I likely would have cooked off several cylinders by now without even knowing why.