All small freeride and slalom boards are capable of 40k peaks in the right conditions on the right day.
Not tried iS101 and F101 back to back, but I have tried sonic 100, sonic 90, iS76 and W53 back to back.
Sonic 100 gave great averages, Sonic 90 gave great top speeds, iS76 was fast than the S100 & S90 on both peak and average speeds. The W53 consistantly beat all by a fair margin.
In 30k winds, small fin, flat water and 115 degree (still fairly tight, 125 to 140 degrees is best), you should easily be hitting mid to high 30k's on an iS101 or F101. But in these winds, you could comfortably be on a small speedboard (W44 style) and be hitting over 40k peaks.
In the water conditions that you describe, iS101 Vs F101 I'd say it would be pretty close, less than 1 or 2 knots difference. Efficiency to the iS101 and easier control to the F101. Both these attribute would contribute to highest peaks speeds for different riders.
But in the conditions you described, for much fast peaks (and fun) you would better looking at either an F93 or iS86 if you dont want to go down the "full on" speed board route