RE: Really need help!..300wby, win mag, or 7mm rem mag?
Why a .30 caliber magnum? You already have a 30-06. The magnums aren't going to do much more, just more velocity with the same bullets for a little flatter trajectory at longer ranges. And, they kick like a mule.
If you want to get belted then make it worthwile, and step up to a 338Win.Mag.
Actually, having fired 'em all I think the 338Win.Mag. kicks a little less than the .30cal. mags, but that was probably more to do the rifle/stock weight & design.
If you insist on a .30cal. mag., then I'd go with the 300Win.Mag. as ammo would be more readily available, and less expensive. The little bit more you get with the
300 Wthby.Mag. just ain't worth it.