fast wide lens recommendation
If you want ultra-fast, then the Voigtlander Nokton 17.5mm f0.95 is your only option really. But then it's $1100 (in Australia) and only has a 64deg FoV.
If you want wider and cheaper, for this application I'd probably recommend the SLR Magic 12mm T1.6 (probably F1.4 or thereabouts). I've seen universally good reviews of this lens.