I don't know much about the stepperworld drives, but be aware that they are not chopper drives. They will require external power resistors, and will generate a lot of heat. If you don't have the drives yet, I would recommend looking at a more modern chopper type drive.
The stepperworld site says the board uses 15 amp rated fet's, but this doesn't really tell you much about the current capacity of the board. The current rating of an fet is specified at a case temperature of 25 deg C, and is much less at higher temps. The fet's will get very hot at higher currents, so the actual current capacity depends on cooling. They are probably only good for 4 to 8 amps.