Fisheye lenses for the Blackmagic Production Camera 4K

Looking for suggestions on the best fisheye lens for the Blackmagic Production Camera 4K.
I want the barrel distortion. Torn between:

Sigma 10mm 2.8 - http://www.sigmaphoto.com/product/10mm- ... sm-fisheye
Sigma 8mm 3.5- http://www.sigmaphoto.com/product/8mm-f ... ar-fisheye
Canon 8-15mm 4.0 - http://www.usa.canon.com/cusa/consumer/ ... isheye_usm
Tokina 10-17mm - http://www.tokinalens.com/tokina/produc ... nhfisheye/
Rokinon 8mm T/3.8 http://www.rokinon.com/product.php?id=200

I was using the 8-15mm on the BMCC 2.5K around 10mm-12mm and it looked great.
Considering the different cropfactor of the 4K, what lenses would you guys recommend?
I could also consider a 8mm if the crop factor of the 4K makes shooting at 8mm look like 10mm on the BMCC 2.5K


Are there any infinity focus issues with any these lenses and the BMPC 4K?

The Tokina is probably 'too good' for what you seek, not fisheye enough! I've not tried the others, but would probably go for the 8mm Rokinon

I have the Rokinon 8mm 3.5 and on my BMCC EF I have to stop it down to at least 5.6 for it to even look sharp, just a fair warning. I haven't handled the 3.8 so have no idea if they improved that function.

Yes, the Rokinon is definitely not as sharp as the Canon or Sigma.

I'm wondering about the crop factor differences between the 4K and the 2.5K. Based on this http://bmpcc.rubenkremer.nl/ I would need to use a 14mm fisheye on the 4K camera to get the same FOV of 10mm fisheye on the 2.5K.