I just finished a feature with FCP X. Finished length was 96 minutes all in one master project. Material was shot mainly with Canon 5D and some additional scenes with Red Scarlet totaling about 25 hours plus lots of 4K still pictures. The editing went super smoothly using proxy media. Never had to render although I had widescreen and S-curve filter on one adjustment layer all the time.
For bigger screenings I switched to optimized media (ProRes 422) and rendered.
I used Macbook Pro i7 late 2011 with 16 of RAM and Lacie 2TB Thunderbolt drive for the material.
I used Xto7 to output the project to FCP 7 sequence for the post house so I had to go little backwards there. For the sound post I used X2Pro to get an AAF of the project.
All and all the editing experience was most enjoyable so far in my career and I’ve used them all since Steenbeck. I must say I like this new storytelling machine called FCP X.