If you really want a new rifle, then I would agree with the 270 theme, but let's face it- what you have now pretty much covers everything you need.

You have more overlap than gap. You could go above or below what you have with a 375 H&H or a 22-250 . Or a 243 or a 458. However you mentioned killing deer in the 230 lb class at up to 400 yards. That won't be just any rifle.
If what you really want to do is slip something in between the 300 W Mag and your 7mm/08 then you could certainly consider a 270 or a 30/06 as has already been suggested. But you are really pretty well set for a wide range with the 2 firearms you have.

I agree the 270 Win would be a perfect choice. That's my favorite WT cartridge. Like I said in the other post the 7mmRM could fit in nicely.The 270 is allot cheaper shooting and will do anything you need it to do on deer size game.

Ruger Redhawk

i don't think there is much of a gap to fill.

The 7mm-08 is too close to a .270 win in my book. Based on what you already own and wanting a long range deer round my vote would be a .257 weatherby in the super ultra version only if you are a handloader. If you don't load I would go with a .270 WSM.

I think that there's alot of gap in the rifles calibers, but in north america there arent any animals in that gap(clearly bigger than deer but clearly smaller than elk). the 7mm-08 is great for deer and your 300 is great for elk + animals. I think your set for those , maybe a varmit caliber?

Looks like you could use a 22 Hornet or a .375-.416

BS