I think you've already been punished by the price of the ammo - what ammo is this and how many in the box?

Over here (Australia) a box (20) of Winchester factory 510gn is $66 AUD (about $60 USD).

I weigh about 160lbs and can more or less shoot 400 grainers off a bench all day (I've only ever done 20 though). I've fired 2 x 5 shot groups off a bench using 500 grainers and they make you feel very un-loved. The 500grainers produce noticeabley more recoil. Although I do use a CZ550 and they are heavy - about 9lbs.

Off-hand I can fire all day long with any load - I gotta make sure I lean forward a little bit other wise I have to take a step backward. This is the same with my CZ550 375H&H.