If you're thinking about something in the .338 Lapua's power range, then take a look at the .338-06. Like I said above, it is hard-hitting and very efficient. If you want to look at another good thumper, you might also consider the .35 Whelen. You can get factory cases and ammo for it and like all the other cartridges I mentioned, it uses the same action and bolt face as the standard 30-06. Also, as I said in my first response, the plain old 30-06 will give you a lot of bang for the buck. With modern components you can get awfully close to the .300 Win.'s performance without excessive pressures. I have gotten up to 2850fps in my favorite 30-06 with 180gr Noslers without exceeding pressure limits, but to be honest I get better accuracy at around 100fps less so that's what I use. Just make sure you work up slowly to what your individual rifle will handle. With all of the cartridges to select from that utilize the same action/bolt face as the 30-06, you've got to be like a kid in a candy store. Figure out what mission you want the rifle to fulfill and the choice will get easier. Again, good luck.
K2