There was a recent post (by Bob Fawcet?)on the 358 (Handloader article by John Barsness) where the author got 2450fps out of a 358 Win with Tac powder. That is brand new data. About 10 years ago the going wisdom was a max 2250 out of that caliber. The same seems to be case with the Whelan - but you must use the right powder & bullet combination. I believe that the 2600fps with 250 gr bullet is the exceptional max & not a given standard. My 9.3X62 Simson does 2550fps with 250 gr bullets but at low pressures with little case stretching. Barsness drives the same bullet at 2700fps out of his new CZ rifle.