Please Please format, otherwise you're gonna hate 2k. You're gonn keep asking yourself, why is this OS so unstable, why is it so slow, why don't certian drivers and programs work, why does it suck.
It's like painting. Scrape off the old paint, then apply the new coat. Don't paint over paint that's already chipping. Won't last and it'll look terrible.
Unless you format, you will not take advantage of all that 2K has to offer.
Good luck with the transition