I would go with a 308 if you didn't have a 30-06, but depending on what you are doing, 243 is a good niche caliber.

Can't really go wrong with the .308 they are inherently a very accurate caliber.

You may also consider a 270. They are a great all around hunting rifle that can take down a deer or even an Elk. That is what I shoot.

What wrong with the 30-06?

I'm confused as to what your are trying to achieve:confused0024:

For long range maybe a 300wm, 300WSM or 300RUM

of the two I would go with the .308

I just love the .308
 

But, for me and where I hunt the "best" is my .444 Marlin or my 12 GA.

The 308 is a great round and really fun if you reload. There are a lot of things you can play with on such a cartridge. As for the 300 Win Mag, hornady makes a light mag 308 round that gives performance very similar to the 300 Win Mag.

I am with some of the others. You already have "long range" capability. What is long range to you? Notwithstanding the capability of the rifle & round, most people should NOT consider shooting beyond 300 yards. Few people practice at or beyond that range. Most people sight in at 100 yards, 2 inches high and hope for the best.

With that in mind, you have 2 rifles capable of that now. I never want to tell a shooter that they do not need another rifle however, unless you have not told us something. it seems that way.

Personally, based on the guns you already own, if you feel you need a new rifle I'd get a .338 Win Mag. But, you already have most bases covered with the current calibers you own.