It is my experience, that once a barrel is truly clean. In my case a badly leaded Yugo SKS with copper fouling under it. It took me 3 days hitting it every hour or 2 to get it clean.
Once I had it there cast was way better, and tended to fill in the bottoms of the pits better than jacketed.
A better lube, continued shooting, it continued to improve until I could with confidence call out a quarter sized piece of orange clay pigeon at 50 yards on the berm and nail them 10 out of 10.
Longer range is going to be tougher. But could IMO still be doable.
I would not advise pushing the speed. In fact bring it down as far as 1400 fps or thereabouts.