It's basically because the a3's bottom end is a little less stable than the a2's. The a2 has a crank balancer and oil squirters that help protect it at high rpms. However there are several on ephatch that run there a3's at 8 grand with k-pro and do fine with it. I would probably run it at 7600rpms if I got k-pro, just to be safe on stock internals. Basically the a2's extra hp is derived from it's ability to rev a little higher. Like I said earlier the tq is almost the same, and as it goes, hp is derived from tq x rpms.