I am looking putting together my first long range rifle, and am wondering on advice on which caliber to get. Have been thinking about 7mm Rem Ultra Mag, but worried this round may be going by the way side. Narrowed it down right now to 7mm RUM, 300 RUM, 7mm Rem Mag, 30-378 Weatherby, 300 Weatherby, or the 340 Weatherby. Any suggestions. Thanks.