I shoot the 6.5x55 in both an original m94 mauser and a tikka T3x hunter. I’ll give you some general velocity numbers and powder used but please work up and don’t assume they are safe in your rifle (they DEFINITELY aren’t safe in the mauser and I make sure to keep my mauser and tikka loads separate.) the best thing about the tikka is I can seat bullets out extremely far since it has a long throat and magnum length magazine, it gives you about 51-54 grains of case capacity depending on the powder.
My heaviest tikka load is a 156 grain oryx at 2590 FPS using H1000- this load has no pressure signs and shoots about .5 MOA at 200 yards. I would feel comfortable going higher with this load but with that sort of accuracy I don’t want to.
Most of my experience with hot loads comes from the 127 grain LRX, which I could never get to shoot great but which got up to around 2900 with R26 before I started to get some pressure signs. At around 3050 FPS I was getting very significant pressure signs and I consider around 3000 FPS the absolute max I would push it that gun/brass/bullet/powder combo. All these velocities are with a 22” barrel.
I know those aren’t the heavy, sleek bullets you’re going to use but hopefully you find this helpful