Depends on your housing, Jack.
I have use the Sigma 15mm on both Subal and Nauticam housings without cut-off with 5 different domes on various FX cameras.
Although to update the data from the linked discussion above:
Percentages of use of two fisheyes (judged from images kept, not taken) - with update for 2012:
All years shooting FX: Sigma 15mm 57%, Nikon 16mm 43%
2008 (D3 mainly): Sigma 15mm 84%, Nikon 16mm 16%
2009 (D700 mainly): Sigma 15mm 72%, Nikon 16mm 28%
2010 (D700 mainly): Sigma 15mm 66%, Nikon 16mm 34%
2011 (D700 mainly): Sigma 15mm 38%, Nikon 16mm 62%
2012 (D700/D4/D800): Sigma 15mm 54%, Nikon 16mm 46% - data unreliable as current shoot where I only have 15mm is unedited.
Comparison of all underwater FX wide angle from 2012, so far:
14-24mm - 3%
15mm FE - 39%
16mm FE - 32%
16-35mm - 26%
Alex