I wouldnt take 612s past 6400 rpms, had issues with float myself, even with them shimmed for pressure. They just dont have the power to control the valves on an aggresive cam at those rpms. Just my opinion. I ran 985s afterwards with much success.

 

ttt I need help with this too. Should i get bigger springs, add a rev kit or ditch the stupid xe cam for a 306.