you'll only lose about 8hp over your sweetspot powerband.  but. 8hp is 8hp is 8hp...  get an itr manifold, call it a day..  btw... I make custom rail fittings for those manifolds so you can use the stock rail with your stock fuel line.  I also make fuel lines for those that need to extend them.  (i.e. CD5 with ATR mani, fuel filter down and on the drivers side, stock line not long enough).