I've had both - actually traded the 35 1.4 (of the Sigma kind, but I've NEVER had any focus issues) for the 50 1.2. The 35 was sharp, even 100% at 1.4 it would always amaze me how good it was. I sort of got bored with it, hence the trade.
The 50 is everything people across the internet report - misses, shifts, etc. It annoys me like no tomorrow, most of the time I'm on the verge of putting it up for sale. But then, once in a blue moon it happens - focus hits and THAT THING RENDERS LIKE NO OTHER.
Yes, I have a love-hate relationship with it