IME string choice makes a much bigger difference on the JC than on most other basses: It's a whole different beast with rounds and with flats. I wouldn't say either is "better," just very different. Flats really fill out the low-mids and turn it into a monstrous low-end groover, whereas rounds really bring out the juicy mids and upper-mids that it has to offer. For me the TI flats are a perfect compromise, and their low tension (relative to other flats) somehow seems to fit the feel and character of the bass. (Actually, I think the ideal would be to have two JCs, one strung with rounds and one with flats.)
So, assuming it arrives with the DM Blue Steels, don't be in a hurry to change them; it'll sound great. Then, consider trying the TI flats (or something else) later on when they need replacing, and you can decide which you like better. (And if you try the TIs and don't like them, I'll be happy to buy the slightly-used set from you!)