7mm08 said:
...there is a difference increase in V and E for the 270 with a W 140g FS whatever that is. ...
I believe that's a 140 grain Winchester Fail Safe bullet.
I think you're not making a precise comparison by using 140 grain bullets for all three calibers. Since these three rounds are different calibers, a 140 gr bullet would have different ballistic coeffecients and sectional densities, and the optimum deer load in each would have different weights.
If you compare the more common 130 gr .270 to the 140 gr 7mm-08, you'll see that at 200 yards the .270 is about 150 ft/sec faster, and has 1991 ftlbs KE compared to 1925. But again, that's splitting hairs. These two rounds function nearly identically in terms of deer hunting practicality.
However, the advantage (in my opinion) of the 7mm-08 is that it's a short action, so it can be in a shorter, lighter gun.
I'm thinking 7mm-08 or .260 Rem for my grandaughter to hunt with.