WOW. I see this thread is long stale, but being both new to the forum, and that the only two high powered rifles I own are in these calibers...I really want to weigh in.
To begin with, I have to say it's refreshing to see a thread where the primary verbiage around the 7mm-08 doesn't include the words "women" and "youth." Not that it isn't a great high-powered for them, as it is. But often when I see it characterized this way, it's done so implicating that the 7-08 is somehow NOT a big time hunting caliber. And THAT, is patently false.
Going back to what I own: Remington 700 CDL DM 7MM-08 and Remington 700 BDL DM .30-06.
The question the original poster proposes is 100% valid when comparing the 140 gr 7mm-08 vs. the 150 gr. '06. What you get for that extra casing is essentially just more in the shoulder (more powder = more velocity). But the on-game performance is practically the same. So if one needs only 140 grains, because the primary purpose of the gun is deer, antelope, etc...then one need not require any more gun than the 7mm-08.
Mine is so accurate...it's scary. Using even factory cheap Prvi Partizan PSP at the range, the gun shoots tiny groups. The gun isn't a fan of 120 gr ammo, which I find no problem with, because it seems 139/140 gr is tailor-made for this diameter in this size case. If anyone wonders WHY, you need only to look at the BC's the bullets offer.
So, the broader point I wish to make is that in that (very fair) comparison limited to 140 vs. 150, I will ALWAYS pick up the 7mm-08 for work requiring that bullet weight.
That said...
What is WONDEROUS about the .30-06, even after 100+ years, is the bullet variety it can deliver. I've always felt (and ballistics tables demonstrate) that 180 gr. is the sweet-spot for it, and this is how I use it -- my Elk gun.
The beauty of the '06 though, is that it can also go from 110-240 grainers with ease. One need only maintain their own 'dope' book for the scope adjustments, and the old joke about only needing one gun is ABSOLUTELY TRUE. IF one were so inclined, you really could just have an '06, using 110's for varmints, 150's for deer and others of similar size and makeup, 180-200's for Elk/Moose/Black bear, and 220-240's for Grizzly/polar bears.
Is it the BEST choice in each bullet weight and game category? Of course not. I can hear the brown bear hunters screaming about their 338's already... But it is COMPETANT in all, and FANTASTIC in others? You betcha.
So...
As long as I can afford to own two high-powered's, I'll use my 7MM-08 for very enjoyable, light-recoiling, hard hitting deer work. And I keep the '06 zero'd at 200 yds with my favorite 180 gr load.
Outside of that, the only other thing one needs is a .22LR of some kind, and you've got every base in the animal kingdom covered (in N. America).
One more thing. Chuck Hawks -- whose sight is probably familiar to many, as he does lots of great articles -- refers to the .270 Win and .30-06 as the "perfect pair" of rifles to cover just about anything (again, other than the .22LR). No disrespect to the .270 (another great round!!!)...but for my money I think that pair is the &mm-08 and .30-06, in part because it's nice to have the shorter action on the 7, and in part because the .270 doesn't REALLY offer a big enough improvement in ballistics over the 7 to warrant the extra recoil.
I would wager, were he alive today, the &mm-08 just might make Jack O'Conner adjust his allegiences.
Oh one more thing. CorBon offers a FACTORY LOAD featuring 168 Berger VLD's for the 7MM-08. The BC is a whopping .617 (!) that is still pushing the bullet at more than 1,000 lb. feet of energy BEYOND 800 yards!!! I have obnly ever seen ONE .308 Win (it's parent) load that could barely match that ballistic performance, and it was another Berger VLD of 185 gr. weight.