It isn't so much the rom as it is the radio you run for your gps to work. the best radio i've used is 3.42.50.
there's a great guide here, I didn't see if you linked this one or not, but here ya go
http://forum.ppcgeeks.com/showthread.php?t=33857
I'm running DCD 3.3.4 and its great! but no you aren't limited to just dcd roms. IMO i've found them to be very snappy and stable.