As far as i know, its not possible to shut down other channel while logging.
Everything is build around a little micro controller, which cant do faster logs than ~10Hz (with current firmware*). While writing to sd-card is one of the slowest processes, actual speed of memory card has very little to do with mooshimeters speed limitations. Actually you might get better results with small and slow card instead of something just found from a store with marketing wank for speed classes with “horse” as a font size.
* If firmware would be written from scratch again only for speed records in mind, it could probably go to some tens of values per second, so basically no real life improvements there.
Many people have confused mooshimeter with an oscilloscope, as we can generate graphs on the fly. In reality, we have multimeter (actually quite fast one), which has a way to show results in human readable form, where “normal” multimeters need to limit updates to ~2-5 Hz so that someone could actually see those values on a 7 segment display.