String guage is a matter of personal taste in feel and sound, so, what strings are you used to and in what tunings now?
As a general rule packs are ballanced to keep quite even tension on all the strings, and as another rule if you change guage by '001', say, 9 to 10, then thats an equivelent tension change to one semitone. So 10s in Eb are about the same tension as 9s in E, if the same brand
P.S. C is 3 tones down ;)