Can you specify what you mean by high ISO performance? Do you mean read-noise or do you mean DR or something else? Canon is very competitive in read-noise and DR. Yes AFAIK they don't have dual-gain in their professional series, but the difference is not "magnitudes better" FWICT.

Read Noise:

http://www.photonstophotos.net/Charts/RN_ADU.htm#Canon%20EOS...

DR:

http://www.photonstophotos.net/Charts/PDR.htm#Canon%20EOS%20...