The difference between the 260 and the 308 is very little as far as 1K wind is concerned. The 260 will drift 5" less than the 308 in a 10 MPH wind at 1K using 142 SMK's versus the 190 VLD running at top end velocities. The 260 will recoil alot less than the 308. The 308 barrel will last much longer. Using the 208 versus the 140 VLD and the difference is less than 3" of difference. Does the 260 beat the 308? Or does the 308 beat the 260? It depends on what qualities are important to you.
The bottom line is that you cannot dramatically beat the 308 by sticking a smaller bullet in the same case.
Now if you want to have a very happy medium between recoil and barrel life and have the least drift, then the 7mm08 running 162 AMAX's or 168 VLD's could be a good way to go. The 162 AMAX will drift 10" less at 1K than the 308's 190 VLD top end for top end. The 208 versus the 162 is about 5" of difference.
Using 140 class (260), 160 class (7mm), and 190 class (308) bullets at up to 600 yards, there is not enough difference ballisticaly (except for energy) between the 3 to even remotely matter.
The link below is a good read.