For most of the factory tubes out there, the 39 gr sierra BK is the King for long range accuracy. It has a nice high BC of .287 and is not to picky with different load applications. The 40 V-max on the other hand seems to be just on the edge for stabilizing in the 1in 12 twist tubes. The odd ones do okay, but alot of them can't get under 1 MOA. I have one 204 that will print out 1/2" or better groups, and another one that is an inch or more with the 40 gr V-max. They both do very very well with the 39 gr BK's.
Here is a link that shows the ballistics, and B.C.'s of the 20's. (Scroll to the bottom.)
Twenty Caliber Cartridge Guide