Both units will perform well offroad - they use the same programs (OziExplorer or MemoryMap both are included on both units)
The way I would rank it having used both for a while:
Slightly better screen in daylight
Faster processor - quicker startup time
Much better on road navigation, maps and program School zone warnings
Better value RRP Vs RRP - includes BT, FM transmitter, 240v charger, carry case, Hema 4x4map collection, OziCE license, Ozi Lite for PC use,
Much easier to upgrade to a bigger card
Its a tough call...