Thanks for the replies. I just got back from the range with the marlin. 14g of unique gave 1400fps with 10fps deviation and a 1" group. Went to 14.5 but velocity only increased 15-20 fps and accuracy started to open.
It is a lot harder to see signs of excess pressure in these rifles compared to my revolver, but with the crony readings, round primer edges, easy extraction, and accuracy like that I should be more than safe.
Thanks again.