I have used Twonky with a GoVideo for nearly 2 years now on an X6. With this said, it has been quite a while since I have tried the generic upnp service. The main difference at the time I converted was Twonky had:
-customizable music/photo/video directories that allowed exclusions
-it read the tags out of the music files/not just the file name
-was much more compatible with my GoVideo than the generic server (less crashes of the GoVideo, never the server)
-searched the entire music/photo/video database extremely quick. (to this day I do not understand how it searches the files so quickly)
My content looks like this, and it has never struggled. All the music is 320kbs, and has never been a problem.
Music tracks: 12316
Radio stations: 0
I think for the money, and the great support Infrant has given to support the software, there is no reason not to spend the little bit extra for Twonky.
Hope this helps.