Inquisitive minds want to know ... 
Some shift registers(like the 595) would solve that and work easilly with the shiftOut() arduino function, so, is it a clock?
I used a latched BCD-7Seg chip on each board so one Extreeme could drive more than the required 5 digits, but the chip/board failed to work reliably without a major rework (effectivly start from scratch) even though on paper it was a good and correct solution. I've thought of shift regs or ather latch logic, too, but choose the BCD-7seg to keep it "simple and obvious" in design. It's not really a clock, even though it counts regulary