How about considering different brand?
Different models of the same brand should be using the same algorithms to process the sounds so I would think they will sound about the same.
If you want a better sound, perhaps looking for a processor of a different brand may be a better choice.
EDIT: I just realized PD is the pandora and POD is the Line6 silly me!

but year i mean if you don't like the PD4, then a PD5 may not be a good idea, a different brand like the Line6 will be a better choice.