I have one particular rifle that prefers mid-list powders run HARD regardless of bullet weight. Often I am well above published data before a high node appears with a 4350 burn rate powder.
The benefit is almost always good groups, low spreads, great velocity, and higher recoil. I almost always stop before I get a pressure sign but I know the pressure is on the upper end.
When a slower burning powder is selected groups go to hell.

The problem is, it makes me nervous. Has anyone else experienced similar patterns?

That would make me nervous too. I have had mostly the opposite happen that slower powders worked better, but they worked well enough that I didn't try the faster powders.

I would see if some other changes doesn't get you the accuracy you are looking for. Keep in mind that with some rifles you are shooting the equivalent of a proof load before you see any traditional evidence of high pressure. I think the number of reloads is the only very definitive traditional test of over pressure loads. I still watch and head primers when doing work up but do not think of them as an actual pressure reading just a warning.

Also how much of a difference are you seeing? I will gladly give up a quarter inch of accuracy for safety and peace of mind.

This is a light barrel hunting rifle so I am not really squeezing accuracy. My goal is always MOA or better with cold bore consistency. Once I have a load I fire an 8 round group that I want to stay around 1 but under 1.5 works. I don’t know how I came about this practice, but it works.

If I can stay under 1.5 MOA with 8, I am confident on animals inside 400.

The rifle often shoots about 1.5 MOA 3 shot group until I push it. Then I will start seeing groups tighten up. Sometimes considerably.

I have a 450 Bushmaster 26” MGM barrel in an Encore. Faster I pushed it he better the groups were. 44 gr. Of Lil Gun and a 200 gr. XPB Barnes would run 2870 FPS and put 5 shots that you could cover With a 50 cent coin. That was spring time temperatures around 50 degrees. Revisited the Load end of August (temps around 78-80). First shot 2869, bulls eye, second shot 2864, bullseye, third shot 3117 foot high, wth!!!! Let the gun cool down, fourth shot 2871 3” high. Huh!!! Fifth shot 3105 never hit the paper. Thought I trashed my VX 6. Shot one more 3078 15” high. So I quit went home. Checked every screw stock to scope all tight so I pulled the gun down. Discovered that I had bent the forend screws and I longed the holes in the laminated wood forend that was just setting on my Caldwell bags. I abandoned the load. Now shoot a 250 gr Shockwave bonded at 2580 FPS and it has repeated accuracy in winter and summer temps. But my barrel likes it fast. Slower loads won’t group as well. The VX 6 was fine. Checked it on 2 different rifles.

Yes, I have several that do this. IMO that's a great rifle, and something that's often hard to obtain, you kind of have to luck into it.

IMO, let velocity and your brass tell you if the loads are too hot with a gun like this. If you're not pushing way past book velocity (adjusted for your barrel length), and are not getting pressure signs and the brass lasts for at least 4-5 loads without loosening primer pockets or other issues, you aren't doing anything too crazy. Nothing wrong with a rifle that shoots best at top loads, that's a gem IMO.

Seems like part of the problem here is the old timer "wisdom" that better accuracy comes with less velocity so you shouldn't use max loads. That works out sometimes, but plenty of times it doesn't, like your rifle.

I've also noticed a tendency to best accuracy at top loads with certain bullet/cartridge combinations with some of the newer powders. Ramshot X-Terminator for example, in several different 223/5.56 rifles for me gave best accuracy with max loads for any bullet 69gr or lighter. That's going back over about 10 years now so not a really new powder, but one of the more modern crop of powders anyway.

If there is no pressure sign's I don't worry about it. Something about pressure, the max load was determined in one specific rifle, on one specific day with specific component's. Nothing say's that the max load would not blow up your rifle or that you can't go by it.

This.

Also, you could be using different brass, have a large chamber, loose throat etc.

When you say "hard", what's that mean to you?

Keep in mind before we had chronographs etc, most of just kept pouring in more powder until we saw pressure signs, then backed of a bit, and sometimes we skipped the backing off part.

Very true that each rifle is an individual. Some like max loads in order to shoot small groups, some don’t.

The business of staying at and not exceeding max pressures is fraught with uncertainty unless a pressure barrel is used. Pressure signs are quite unreliable, such as primer flattening, case head expansion (the late Bob Hagel’s favorite) and sticky bolt lift, are shots in the dark. Some are swamp gas (such as case head expansion), while others simply indicate excessive pressure (excessively flattened primers or sticky bolt lift). On the primer indication, I have many times encountered a load that was too hot (indicated by hard bolt lift and higher than book velocity) but whose fired primers gave no indication of too much pressure.

The closest without a pressure barrel is a chronograph and load data. Pressure and velocity run together, so a listed max (velocity) will roughly equate to max pressure. Not perfect, but as close as we get. The indicators simply don’t work very well.

ANYTHING I've ever ran a mono bullet in, seat em deep, and drive em HARD!

Are you using the bullet weight you want, vs. what the gun likes?

I had a 270 like that - it hated 130’s unless I over ran the loads, but it loved 140’s.... I didn’t want 140’s so I rebarreled it.