Before I had the SOS SC installed I did some research on extrude honing.
I first learned about extrude honing when I had the RX7 and people were talking about doing that to the engine ports, manifolds, etc.
It seems that with regards to the NSX heads, extrude honing on a stock displacement and stock compression ratio block will yield very little benefits if any. That's the jist that I got from STMPO, Driving Ambition, and Lovefab.
I called an extrude honing shop and the verbal quote last year for the NSX heads were $1500.
If you are going to do head work you may want to consider probably the best valves ever made.
I have the undercut valves for the GTO when I did the engine rebuild to handle more power.
Same thing here. Did tons of research and after learning that most of the Supra guys making serious power north of 1000HP I was convinced that these were the valves to get.
The big selling feature and benefit of the Ferrea valves is that they seem to be the only ones made so that if you over rev your engine or if the timing belt were to bust and the valve and piston were to kiss, the valve heads are the least likely to break off and bounce around in the engine causing even more damage. They just simply bend and keep the damage localized to that combustion chamber.