Finally getting around to checking RPM versus pulse width on my test stand, I found that the High RPM mode of the ICE 50 gave RPMs considerably higher for a given pulse width than did the previous Phoenix High RPM mode. For 15% throttle (1.15 ms), it was 7710 versus 7200 for the old calibration, and the difference increased to about 1000 RPM at 55% throttle, about 12,870 versus 11,770 RPM for the old calibration. This shouldn't be a problem with any of the timers out there -- you'll just get more RPM than previously, for a given throttle setting.