I agree with the 28 Nosler. If you like the 7mm family it is an awesome cartridge. I am running Retumbo under a 180 Berger and it is an awesome shooter. Easy conversion from the 300 RUM, and will be a great gun.
Why not a 30 nosler? You'd stay with a 30 cal with better barrel life than the 28. Retumbo will work however it may not be optimum. I know there are better powders for the 7 mag but in my brothers 9.5tw. Retumbo and the 162amax are surgical at 3030fps. I can get more speed with Rl26 but not nearly as consistent in the little bit of testing I did.