If you get it now, it will be 3.7, not 3.8 -- I think 3.8 will first hit when the Charm is released. As far as waiting -- it could be a long wait. We keep hearing Q4, but Q4 is a big chunk of time
And it's a piece of cake to upgrade to a newer OS -- don't wait on the OS, but do consider waiting for the new devices (7100t or 7290) -- much harder to swap out hardware