I have found one of each and am torn between the two. I have never seen a Haro in person so have no clue about them. I ride a mid 90's Trek 820 and want to upgrade a little. The V4 is a 2006 model and the 4900 is a 2004 model.
Short list of specs. Haro has disc brakes and Trek has rim.
Fork Rock Shox Pilot C, 80mm travel
Shift Levers Shimano Alivio RapidFire
Front Derailleur Shimano Alivio
Rear Derailleur Shimano Deore SGS
Crankset Bontrager Sport, 22/32/42 teeth