Jay,
In HG class because you have the weight to work with when using a true HG, and not your LG in HG class, any of the 30 caliber magnums have firmly establsihed themselves in the accuracy department and have been known to do a little killing on the other side of the county also. So they are essentailly the best of boths worlds for target and LR hunting.
Seeing how you have a 300 Weatherby already in LG (and it's working real good!!) I would recommend staying with it for now for both rifles. The 300 Weatherby isn't an ULR caliber, but you can still kill deer sized stuff well over 1000yd with it if that's up your alley. Plus the added benefit of using a known good caliber while learning and setting up a true HG is going to save you a lot of headaches over chasing a new rifle/rest setup as well as trying to learn and tune an unknown caliber at the same time. That's a tough road for a new shooter.
Hopefully if work stays somewhat even keel for the rest of this week, I'll see you this weekend at Quantico! Look me up. I usually setup with Phillip Yott right at the top of the stairs and veer to the right.
Steve