Everybody, his uncle and his sons dog have figures for these guns and you can quote from the now until the end of history without really solving the issue. The solution to the problem lies, unfortunately, in the primary sources, i.e. those produced in context with the firing test, calculations and estimations of performance. And as far as I know, no one have managed to find anything conclusive on the matter of the many different muzzle velocities registered for these guns.
I dont want to discourage discussion, that always turns up some interesting snippets of information, but the issue of muzzle velocity is complex (conditions of test, propellant used, age and condition of ammunition used etc.) and the issue of penetration on top of that much more so.
But as long as the differences between figures amounts to less than 10%, it hardly matters in game terms.