Did you look at the 270 wsm ? It's around the most versatile cartridge you can find, and it has the same recoil as the 06. I use mine for everything I hunt, Deer, Elk, Bear, and pronghorn antelope. It rocks! very very flat with lots of knock down power past 300yds, and not alot of recoil.
My vote is for the 7mm.08. You are dead on correct that it can be loaded to be one helluva wicked round. Accurate as can be (mine is anyway) with pleanty of power and very limited recoil. So if its for your nephew (im assuming he isnt grown up) then the 7.mm08 would be a perfect calibre to get. Love mine!!
There can be too much of a good thing with antler rattling.
I like to hit the horns together for a good 30- to 40-second rattling sequence and then hang them up and resist the urge to hit them again.
This works to the hunter's advantage, because if a buck has heard it, he may have been 300 or 400 yards away and he comes in and he's not exactly sure where it came from.
When finally is time to rattle again throw a slight change-up into the routine.
The second time, don't rattle as loud...