Not sure if the 3400 fps load was hot... no pressure signs whatsoever. However, I would never use somebodys data (including mine) just thrown out there over the net. ALWAYS research the loads with the major powder companies to find what the safe ranges are, then ask around to see if there seems to be a sweet spot within that range. It goes without saying, back off a few grains the first time when loading for your particular rifle and work up.
Those velocities were through my chrono....no telling if that's accurate. Of course it says my .280 with 140 grainers near max book charges are only 2800fps, so I don't think its consistently reading high.
The advantage (or disadvantage) of the RUM's is that they're so overbored you've got to have a long tube to burn all that slow burning powder. It's an incredibly inefficent case, compounded by using it in 26 inch and under barrels.
The RUM's really begin to shine at a minimum of 30 inches of barrel length. They are one of the few cases out there that the velocity goes through the roof just by adding 4 to 6 inches.