I'd be tempted to split with 4 of each.. A12's and N72's. These are similar (very) to the classic API and Neve mic pre's used on countless hit records. With 4 of each you'd have quite a lot of rock history sound at your disposal.
I personally have 3 N72's but have built at least one of all of the pre amp kits and I must say they ALL sound good! But if it's strictly rock then both the N72's and A12's will... errr.. rock.
The previous poster's suggestion would of course work well. Personally I'd probably want more N72's but that's just my preference. Definitely get some of each of the N72's and A12's though. You could consider 3 of each and then still 2 J99's. That would rock well. You'd have lots of options that way.. the J99's would be great for drum overheads.. and a lot of other things.
Commodor