Get it you will not be disappointed!Focus is only slow from MFD to infinity and i personally do not think its slow for what i use it for.
I do not want to take away from the 85L as it is a superlative lens, but it is the slowest focusing L lens I know of under 200mm.
If one is willing to give up a bit of sharpness for focusing speed, versatility, and less bulk/weight - the 50L may be a better choice.
If you are using the lens for events or anything that requires quick focus or tight quarters, the 50L is better. For straight portrait work where you have control over the target the 85L is better.
Here is a video made by photographer TIM NOSENZO comparing focusing speed of the 50L to the 85L:
The 50L is not quite, but almost twice as fast compared to the 85L in focusing speed.
It is actually great to own both, really a question of the specific application which one would use more.
I never said it was the fastest,but this is the portrait lens and it does that very well IMO it produces photos that no other lens can,its a specialty lens if i want fast focus i have the 70-200 mk2 which is fast but i have had no issues with the 851.2
My advice rent it and use it for a week