Well, **"Must you" is much more formal and as such rarely heard in speech** {SPOK at COCA} these days.

E.g. at [COCA (CORPUS OF CONTEMPORARY AMERICAN ENGLISH)][1]

. DO YOU HAVE TO
 
in [SPOK]

52 hits

. MUST YOU

in [SPOK]

0 hits

I am using the "." as part of the query to look only for sentence starts.

  [1]: http://corpus.byu.edu/coca/x.asp?r1=&w=1120&h=700

>-

At the BNC (BRITISH NATIONAL CORPUS):

. must you

http://bnc.bl.uk/saraWeb.php?qy=.+must+you&mysubmit=Go

3 results