Canon 1.4x TC -- II or III ?

I'm using a 1.4x II with my 7D and 300mm/f4. Would there be any benefit to upgrade from II to III?

Not much Randy. If you pick up one of the new Canon supertelephoto lenses, then maybe the AF will be more accurate. But optically it's not much different than the older version. Have a look at this thread.

Ditto What Doug said. Very little difference with 300 f/4 lens

I find the new 1.4x has slightly better contrast than the older edition. The new 2x is without a doubt better in many ways, and worth the upgrade.

Chas

I had 1.4x II which I sold and bought 1.4x III . Frankly speaking found no diff in IQ with my 400/5.6 and 7d