You've probably used up more battery power by shutting down SmartReflex than what you save by moving the OPP Voltage Target.

SmartReflex is calibrated at production, and on the OMAP3630 HS as used on the N9/50, SR Class 3 automatically targets the lowest voltage possible when enabled. It also shuts down unused portions of the SoC to save power.

Undervolting is pretty much moot - it had some impact back on the N900, but on the N9/50 it's pointless.

I do not know if the SmartReflex values on the N9/50 are calibrated for frequencies beyond 1000MHz, but if they were, it should keep working (at least until the highest factory clock speed OMAP3630 goes to - 1200MHz)