This is exactly how I have it wired up...
and as you use ss 10 , 9, 8 and 7..
I use 53, 49, 48, and 47 (Because 50 - 52 are the other SPI pins)
I'm just torn between what we have and what this playground site says to do:
http://www.arduino.cc/playground/Main/MAX72XXHardware
its saying the Load and Clk are in parallel but the data (MOSI) needs to be cascaded for the syncing into the next matrix...