Ed,
You have to consider that you have a limited area you can remove with the water jackets so that is a limit on how much you can shave the heads. Why many are only taking 20-25 off the 16/17's with the 117 kits. On the 117 for instance all things being equal most are seeing 120/126 range add 7 with a typical 1.10 to 1 upgrade on headwork cubes and you end up 128/134. is it close yes, but those extra's cost money and all the parts being right. Not saying it wont happen, just caution in the wind to not get oversold. Would want to see dynosheets from the same dyno without and with headwork to not see the overall numbers but actual gains.
'Totally Agree,,,
I was thinking more along the lines of Cam, Exhaust, Piston (Dome) and Port Development for the 4 Valve / Dual Plug M8 ,,, not necessarily shaving the Heads... When there are 2 Points of Ignition,,, Domes might become more "friendly"