Cecil’s column: http://www.straightdope.com/classics/a2_153.html
I think that the writer of the first Site for sore I’s has it right, 4 slugs of X, V, and 5 I’s. However, I think he has the order wrong, and that giving the right order will quash Cecil’s concern about clock numbers not being made from individual letters.
I think the order should be VIIIIIX. Note that while the V is not rotationally symmetric, I and X are. So, the four slugs would be divided something like this:
VIII-IIX
VII-II-IX
VI-III-IX
V-IIII-I-X
You can rotate/flip one of the IX pairs around to become an XI, and you now have all the numbers you need.