There were many improvements that were made with the release of the Version 2 machines, including:
Thicker gantry uprights
A taller and more robust X axis cross extrusion
The speed was increased from 30 mm/sec to 50 mm/sec
Each axis is supported by 4 track rollers on V2 rather than 3 on the V1
The motors are larger
The lead screws are larger with a more aggressive thread pitch
The Z axis is taller on all V2 machines, and the 420, 600 and 840 are even taller than the 300
The Z axis tool holder plate is longer to support larger spindles like the Kress 800