For image quality, which would you prefer/recommend: 6D (FF & low-light capability) with a 1.4X converter or the new 7D2 (at native resolution, without a converter).Just a word of warning, you wont be able to use the 1.4x with the 50/1.4. From Canon website for the 1.4xIII:
I have the 300/4L, 135/2L & 50/1.4 - it is the 50mm performance that I am most interested in (70mm @ 2.0 with converter, versus effective 80mm @ 1.4).
Note: This lens is only compatible with fixed focal length L-series lenses 135mm and over, as well as the EF 70-200/2.8L, EF 70-200/2.8L IS, EF 70-200/4L, and EF 100-400/4.5-5.6L.To get a focal length around 70-80mm you will need to get a new lens for a full frame camera - if that is what you want or need. This may be a factor in your final decision which body to purchase.