I wouldn't be bother spending good money to upgrade from DIGIC 4 to DIGIC 5 because there isn't enought improvement to warrant the costs, unless the OP need AF speed and is making money with the equipment. And, the other bonus is that the 50D is better than its younger sibblings when you use Magic Lantern
http://www.eoshd.com/content/10770/canon-50d-magic-lantern-raw-review .
And, perhaps the OP might want to upgrade the firmware to newer version to take advantage of larger capacity and newer CF cards.
<--- Purchased Canon 5D mkII with less than 30 days before the 6D released but I couldn't be bothered to return the 5D II and wait for the 6D, because I don't think there isn't much of a different between DIGIC 4 & 5 to be a concern.