as far as capacity goes, any short mag is gonna hold less shells, bolt or auto loader. it sounds to me like you have some wide open shooting where your located. i would sacrifice the 2 extra shots for the performance your gonna get out of the .300 WSM...its awesome, you wont be dissapointed. the .270 WSM is another great performer.
now, the one shot one kill thing, we should all stive for that. but, on occaasion a follow up shot is required. but, IMHO, if you cant kill it on the 2nd or 3rd shot, your probably not gonna kill it with the 4th or 5th...MOST guys are just aimlessly flinging lead bu then. :pissed:
as far as the scopes youve given us to choose from, i dont think you can go wrong either way. both quality products. i have a bunch of monarchs...i love em.