I shoot the 5dmk3 and I use the Tokina 10-17 with a 1.4 TC. All the wide angle shots here: http://stewartsy.com/anilao-2013/ were taken with that combo. I used the combo behind the Aquatica mini-dome (4"). The lens was usable from about 12mm-17mm. I've printed some of them to 16x24 and the quality is outstanding.
Nice shots, did you also use the 5D3 for the macro (100mm) ?