Love the 460 on the G21. The gun's big enough to keep control of this beast and make it genuinely fun to shoot...I hear you on the "palm slap" though. It'll make a man out of you.
Regret the gen4 super-stippled grip texture at times. Seems the smoother gen3 grips would be easier on the hand. Oh well, the thrill of the KABOOM from this hand canon is well worth the adjustment. I can't think of a gun that's made me want to invest in water jugs and watermelons quite this much.
Hard to beat hand loads, but the 460 is definitely an amazing round ballistically...even with off the shelf ammo. I love how much fun this guy has (good real world test data too):