Which is faster: md5() or hashtext()?

G'day,

I need to do a mass update on about 550 million rows (I will be breaking it up
into chunks based on id value so I can monitor progress).

Hashing one of the columns is part of the process and I was wondering which is
more efficient/faster:  md5() or hashtext()?

hashtext() produces a nice tight integer value, whereas md5() produces a fixed
string.  My instinct says hashtext(), but there may be a lot more to hashext()
than meets the eye.

Any ideas?

Thanks
Henry