The .250/3000 is a good analagy. The 6.5x54, even when held to lower pressures due to the dovetailed ring, will exceed that smaller case's, factory 53,000PSI level ballistics.
They would be a reasonable level to use for loading approximations + perhaps 100 to 150fps or so for the larger diameter bullet and greater case capacity.
-------------------- Daryl
"a gun without hammers is like a Spaniel without ears" King George V