i'm sure you can find tons of that if you google for it.
I personally find that the f1.2 is much better than the 1.4 in terms of handling and balance. After all, it's a L lens. As for IQ, the bokeh and colour is much better than 1.4. Though this is from what I can see with my eyes. Not some technical chart or software measurement.
If you were to ask me, I'll say go for it if you have the moola.