Good catch... previous numbers changed...
With new numbers FB does about 25% more dps then kensai up to 45AC, and they do equal at 55AC
With +1 multiplier for kensai, FB still does 15% more dps then kensai up to 45AC and do equal at 51AC
While a hasted kensai only does about 5% more dps then FB.
This is why i like multiplier... it helps balance out weapon choices and closes the dps gap enough to be comparable but not come too close as to tick off any barbarians who would be outraged if something could actually out dps them