As others have said, the 6.5mm Rem Mag's bark was worse than its bite. Recoil was OK, but the muzzle blast out of the short barrel is stunning. I think Remington was trying to invent the short magnums when it started marketing the 600 and the later 660 and Mohawk rifles, the rifles were short action, short barreled, and the dog-leg bolt handle was just flat ugly. The standard calibers it was chambered for lost a bit of performance due to the short action and short barrels, but the magnum cartridges suffered much more due to deep bullet seating to fit the short action and velocity loss due to short barrels. In a longer barrel, performance for the 6.5mm Rem Mag is actually pretty good.
The only chambering in the 600 I can say recoil was bad on was the 350 Rem Mag, and muzzle blast and recoil were harsh in a 6 lbs rifle.