You haven't seen any problems with the valvetrain at those RPM? more specifically the lifters?9000rpm is attainable on a stock 5.0. Cams and Ported heads and long tubes will allow 9500 which is the limit of the vanos pump. You don't really want to go past this as you don't want to remove vanos the engine will make no power. There is a 6.0 stroker of mine running 9200rpm essentially no limiter. Has titanium rods, billet lightweight pistons, shrick cams, springs, larger valves, ported heads, supersprint long tubes, 880090 thermostat. The only way to make power this high is with a 305 duration camshaft.