I don't think you will see a huge difference. The DHXs' are pretty good. I went from a Vanilla to a DHX and notices a big difference, but the DHX is a big improvement over the Vanilla. A lot of money to spend on a nominal improvement IMO.
I have been pretty happy with the DHX 5 in general (on a DHR, Sunday, pack for a short bit), but the 'pack' now has a cane creek db on it and it feels very good (LOTS of adjustment...you can set it VERY bad if you want..). I would however been perfectly happy with a DHX on it if I did not get a great deal on the DB (and personal curiosity to try it)..
There are many adjustments on the DHX, and it takes a while to play with them all (independantly) to figure out what effects each has. If you have not exausted/systematically tested ALL of the parameters of the DHX, you should do that before spending the $$ on something else.