Since you have the 30 cal covered with the 06 and as well own a .243, with a 100-300 yard mark on deer you have lots of flat shooting choices. Sounds like you want a mag so to spread it you could look at a 270wsm or 7mm rem mag. This would add some diversity to your gun cabinet and both would be able to handle your requirements on any given day.

I use a 7mm rem mag for deer(WT and Mule), elk and moose it has had no problems taking any of these game at varing ranges. Lots of bullet choice for the .284 and OTC 7mm rem mag ammo is readily available if you buy factory loads.