Go for book data with retumbo or rl25 to start with.
I'm using retumbo with 171-175 grain bullets in my 7rum.
I had a prior 7rum shooting well with 95 gr rl25 and 140sierra or nos ab.
With the 140's I'd start a work up with the goal of 95 gr rl25 using rp brass and 215's. Load to max mag length... around 3.650" on most remmy rifles
If you want to work with rl50 I'm shooting 168 berger vld's on top of 95gr rl50 lit by a 215; it seems like a good load so far but hasn't been pushed to the max.. You may get to 98gr with a 160 with no issues... work up of course. I haven't chrono'd yet but it shoots well in my pipe.