I know I'm late to the game, but I have a 50mm 1.8 that has a problem with my 6D that AFMA can't fix. Just bought the 85mm 1.8 (love it) and was considering a replacement for my 50mm 1.8. I thought it was going to be the 50mm 1.4 but after reading all this, I'm thinking I'm going to wait. Might buy the shorty 40 while I wait for Sigma to actually give us a price. If the new Sigma is as good as everyone thinks its going to be, and it costs under $800, I'm there.
I'm also very interested in what the Sigma will bring - and I'll definitely be reviewing it when it's available. If you can get the 50mm while it's on sale for less than $400 I think it's still an incredible value. Despite my "ho hum" review of the 40mm it's kind of grown on me, it's a very capable lens and if you don't have a zoom in that focal range it's a no-brainer as a buy.