Originally Posted by rparmar 
No-one ever went wrong buying a fast 50.
Strange thing is I have never bought one. So I hope there is no corollary to my first statement!
I agree. I had FA50mmF1.4 and I tested it out with my F50mmF1.7. They are close really in everything.
This is from F50mmF1.7 at F2
At the end of the day I traded my FA50mm away just because the F version has a more classical external appearance. More old fashion Japanese engineering taste. Not because of the optical qual. That is it.
Daniel