Big Tom,
I would be very leery of any advice received from anyone who considers a .300 Weatherby to be barely mid-range for big game. :?: Obviously, owning a gunshop doesn't make one an expert.
Your .300 - with proper bullets - will work fine for anything in North America and most stuff in Africa.
Doesniper and huntsman have made some very good points.
Consider a good quality .22 LR to round out your battery.
If you can handle the .300 Weatherby with 220 grain bullets, you should be able to handle the .338, although the .338 really won't do anything your .300 can't.
I used a .338 Win. Mag. for awhile when I lived in Alaska and discarded it. Went back to my .30-06. Used my .375 H&H if more thump was needed. Later on, I tried a .35 Whelen - use that and a .358 Winchester quite a bit now. I used to be into high velocity magnums, but no more. The .358s are good out to 300 yards which is as far as anyethical hunter needs to be shooting at unwounded game. From what I've seen, shooting at game long distance reveals a lack of stalking skills, knowledge, and character.
It's doubtful if the 7600 in .35 Whelen could match a bolt rifle for accuracy, but with you're .300 Weatherby, you really don't need a Whelen.
My :money: worth.
Rocky