Personally, I like to stay in the 1150 fps range for everything I shoot, except steel, even modern loads in my Perazzi MX 8. High muzzle velocities are very misleading. So many people think that it significantly cuts the amount of lead you must see on birds/targets. The difference is so insignificant that you'd be better off worrying about the relative humidity affecting lead.
It is solid physics that the faster a projectile leaves the muzzle the faster is slows down. IOW, a load that leaves at 1100 fps is not 100 fps slower, at 30 yards or farther, than one that leaves at 1200 fps.
I agree with Mike K. 100% about what is most concerning with these old guns .......... it's the wood that goes first. I've only seen one damascus barrel ruined by overload, and I warned the guy not to use that powder/wad/hull combination before he did it.
The chamber opened up ruining the fine old Boswell double. He claims it was a base wad separation from the previous shot. Nah, obstructions don't blow out the side of the chamber, they damage the barrel just before the obstruction. it may be remotely possible that the base wad lodged in the forcing cone, but I'll never believe it. I know what he loaded into those shells, because he told me. This is the same guy who put a 100 hp Subaru engine on a GyroCopter to get more rpms, resulting in throwing a blade off the prop, which resulted in an ignominious landing. He just has to push the limit on everything, ofttimes much to his chagrin.