Yes, the the 270Wthby will have higher velocitiies than the 270W. Often when comparing the Weatherby's to standard chamberings barrel length is forgotten. When comparing velocities it helps to compare equal bbl lengths.
Carrying my heavy-azz MkV's hunting never appealed to me (although you're talking about revamping a M700), and shooting a 270Wthby in a sub 7lb rifle has never appealed to me either.
The highest velocity with a 270Wthby and 150gr NPt in the Nosler manual is 3207 fps with a 26" bbl. Nosler velocities are rather consistently....ah....optimistic.
As others have mentioned, RL-26 in the 270W has upped the ante a fair amount. Given Alliant's data and what I have chronographed, the 270W may be the biggest beneficiary of RL-26, consistently clocking over 3000 fps out of 22" bbls with 150gr NPt's
In other words, when comparing equal bbl lengths--and reasonable pressures--there is about 150 fps max difference between the two cartridges, often less.
I have a 25" Douglas barreled M700 in 270W that already thinks it's a 270Wthby. It is on my short list to get the RL-26 treatment.
