A thoroughly unscientific opinion is that on my recording devices, on my computers, with my flash media, my CF's are faster than my SD's. But that could also be due to a wide number of factors and shouldn't be considered a rule.
I really don't think it matters relative to the ultimate question: How is your school going to use these? If the recorder is specifically for SFX shoots, sure, a 702 is economical and does use CF cards. If you're recording multiple tracks of dialog during actual production, then you should use a 744 (where the CF card is more for a safety backup) or the 552 (which tops out at 96kHz, unlike the 744 which tops out at 192kHz)...or any number of other options, including the Zaxcom Nomad, Nomad Lite, or even a used Deva.
UPDATE: Checking some quick websites it seems that indeed CF cards in devices have a general 2x to 3x speed bonus over SDHC cards of similar capacity, at least in cameras. Seems to me that as long as the cards can keep up with the data rate required - not hard with audio, as compared to video - the only gotcha is transfer speeds from device to editing computer.