In an effort to squeeze extra horses out of my Supra, I planned on getting the head ported and polished during the engine work.  I knew that it wouldn't cost too much more (in labor and machine costs) to have the head prepped for larger vavles.  I am installing a set of Ferrea 1mm oversized valves, dual springs, titanium retainers and new spring seats.  Ferrea's under-cut valves are pinch rolled to reduce the stem diameter just above the head, where other manufacturers machine off material.  So far this has been the most expensive addition during my rod knock rebuild. 

Right now these are sitting on my shelf waiting the money for the engine work.

1- None for me yet

1- The cost.

The obvious payoff will be in the added size of the intake and exhaust openings.  This is a combination of the larger heads and the pinch rolled stems which reduce the stem diameter in the port area.  The dual springs are probably not necessary right now, but extra closing pressure will be important should I ever go with aftermarket cams.