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I vote 2 valve. I reason that if 4 valves is tuned to make peak hp at 6000 rpm and peak torque at 4700 rpm, then 2 valves will tune to half that (for the 2.4 ecotec). peak VE will now occur at 2350 rpm - which is my cruise rpm. It will make more power at that rpm than stock - which you confirmed. Polishing the ports and chamber always help. Also, running one exhaust valve means there are fewer hot spots to cause knock. 2 intake valves cause a tumble motion, while a single valve causes strong swirl - potentially better against knock.
I would also reduce the intake manifold runner area by 50% to boost VE. A 6" runner will actually help. A turbo will boost FE and regain the top end. My .02
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