I am very happy with the FCP X editing experience as such and as it truly aides my personal working-style to free up the way I work in a timeline...
...I am however deeply unsatisfied with the performance I am getting out of my system. Could it truly be, that my system isn't up to the task of running this App fluidly? Timeline scrolling and scaling is stuttery, opening things takes a long time...
I had above system like you only with a GTX285 Card inside. I had a RAID0 spinning drive system.
Performance in FCPx sucked and so it did on a much newer and bigger Mac Pro.
As I always do when a new MacPro pops out, I go and get it. Call me an addict. I got the Retine, 2.6 & 16GBRAM with a 512 SSD.
I tested FCPx on that... And let me tell you, it is so much faster than the MacPro. Unbelievable. I could not believe my eyes when running a project
off of the internal system drive. FullHD ProRes 4444. I can even play RAW Image Sequences. OFF THE SYSTEM DRIVE ;-)
Anyway, I believe in the faster CPU and care less about size... I have a machine room in which the coomputers are residing. I took the retina and put in on top of the BIG Mac Pro, closed its lid, put the 30 Inch Cinema Display into a thunderbolt port and a 1080p monitor into the HDMI. 2nd thunderbolt port is used for an external SSD. This setup is so fast and so is FCPx. It beats any current Mac Pro regardless of RAM.
Ok.. After this very long anecdote - Here is my answer to your question. Yes, you CPU is too slow. ;-)
Wish I could say, buy more RAM - put an SSD inside... But if I did that you would be wasting your money.
QUite a few of my colleagues were laughing as I told them the story above... Their smile quickly vanished when they saw it for real. The Retina is IMO the first super computer Apple has ever built and I have been using Apple since 1995