Both Kitprog3 and the Miniprog4 have the same firmware, hence there won't be any speed difference. Miniprog4 is essentially Kitprog3 hardware itself but with additional protection circuits needed for programming (i.e to avoid failures due to over voltage etc.).
Hence, Miniprog4 too doesn't support USB high speed, it uses the PSoC5LP which has only USB full speed support.
Thanks for info! Is there a schematic available for Miniprog4?