I currently use both the 6D and 7D bodies with a EF 100-400mm, the EF 70-200mm f/2.8L IS II USM +1.4x III combo and the Tamron SP 150-600mm F/5-6.3 Di VC USD A011 for air shows. With out a doubt the EF 70-200mm f/2.8L IS II USM +1.4x III combo is my favorite. So much flexibility with this lens and either the 1.4 or 2.0 extenders, plus the IQ is out of this world. The Tamron is good, but almost to much lens in a lot of cases and the IQ doesn't quite match either of the Canons. A few samples -

EOS 6D w/ EF 70-200mm f/2.8L IS II USM +1.4x III combo

Bombs Away by davidfranks319, on Flickr

Wings of Blue by davidfranks319, on Flickr

EOS 7D w/ Tamron SP 150-600mm F/5-6.3 Di VC USD A011

From the Top by davidfranks319, on Flickr

EOS 6D w/ EF 100-400mm Dust Pump

"Spirit of Texas" by davidfranks319, on Flickr