bigpapa - if you have a 30-06 there is no need for a 300 mag. Yes it will be more potent, but not too much. If its a 'cannon' you're looking for then start looking at the 338 Win Mag and up.
If you decided that a 'big' gun isn't for you - and by looking at what you have, you may want to consider something a bit easier on the shoulder. If you pan on just punching paper or varmints then something like a 22-250, 223 or the like. If deer sized game is on the slate then something on the order of a 260 Rem or 7-08 Rem.
Let us know what you decide.