Right now my favorite 338-06 load is a 225gr Hornady SST over 55gr of RL15. According to my notes the 5 rounds I ran through the chrono when I was working up loads registered 2645, 2634, 2666, 2666, and 2647. This load shows no pressure signs in my gun but depending on what load books you look at this is VERY close to a max load so definitely start low and work up. Most books use the same load data for the interlock and the SST so this will give you an idea of what you can expect. This wasn't the fastest load I tried but the numbers were consistent and it grouped nicely.

I'm trying to find some Vhitavouri N550 to play around with. I've heard that N550 works beautifully with bullets in the 225-250gr range in a 338-06.