Okay, I'll saddle up to this query.
Get the G20 if you want to hotrod!
Now sure you can go and get a G21 and then get a wildcat conversion barrel and pay through the nose for those semi-wildcat rounds--btw, the .40S, 460R, 45S are semi-wildcats.
And why? You could get the G20 and have all you'd need!
With everyone manufacturing 10mm ammo in all levels of power--tepid to titanic, there's no need for a swap out barrel for hotrod performance.
But if you are looking to keep the pistol stock, I can find .45acp ammo everywhere but I need to order 10mm ammo for my tens.
So in that regard the .45acp G21 wins hands down.
Derek