The 322 is a pretty capable unit for it's size and will do the job. Soil conditions play a role in how long it will take you. Around here water lines fairly shallow (36 inches) and the ground only freezes about 12-14 inches.
If you're talking commercial work a larger machine would be more appropriate from a time standpoint. However, if your query is for a couple jobs around the house the 322 is adequate. More specifics on your particular job(s) and conditions would help a great deal.