Actually, my last tests were on a Feather MO Adalogger (using the integrated micro sd slot, 48MHz processor, should be 24 MHz SPI clock).
I just got done getting my Feather WICED running, and benchmarked the same cards with it and the Feather M0 using the same micro sd breakout board from Sparkfun (Wiced has a M3/STM32F2, 120MHz, should be an SPI clock of 60MHz available...) and got worse results, by 60-80%, with the M3 than with the "slower" M0.
results:
