I've used both a sigma 1.4 and the 2 and both provide less than perfect results with my 120-400mm sigma lens I would describe it at soft and softer never really happy with what it produces. Although it is manual focus so could be me I suppose but as sharp as I think I have it it always seems soft.
The 1.4 on the sigma 70-210 f2.8 on the other hand is an excellent combination and works well.
