This much is true. Lower bullet to bore friction will mean less of the energy/pressure the powder generates will be consumed/expended fighting friction/heat, and more will be available to increase MV.
Given equally well suited (ideal) powders for any two different bullets of the same weight, the bullet with less bore friction should always be able to be driven faster than the bullet creating more bore/bullet friction. This matter is well proven by shooters that HBN coat their bullets.
The only thing remaining unknown is the magnitude of the velocity loss that will result from the additional bullet/bore friction. It may not be a big deal or anything to fuss about. I provided the one relatively recent example of the 210 VLD versus the 215 Hybrid comparison because both of those bullets have been in heavy use now - the newer 215 Hybrid for several years, and the 210 VLD for many more years. The track record on MV is clear. The 215 Hybrid with its shorter bearing surface is consistently being driven to a higher muzzle velocity than the 210 VLD, even though it weighs 5gr more, and even with the use of the same/identical powder. Broz may be the member with the most first hand experience, since he's an avid user of both bullets and loads and shoots so much. He also gets feedback from others' rifles that he's involved with. Explanation = shorter bearing surface = less bullet to bore friction = higher MV.
Coat the bullets with HBN, reduce the friction a little more, and gain a little additional MV; all in the very same rifle. Which does away with almost all of the other possibilities that could be influencing/increasing MV.
Where do I get them?! 
