Many thanks for your responses - which largely confirmed my hunches. It seems the MPB solution (as described on your blog) is the answer. When I price out the comparison of Retina / Non-Retina there seems to be some argument for the Retina. Both machines below retail at $2499.00.
You loose the SuperDrive and Firewire port with the Retina but gain a second Thunderbold port and a 2.7Hz vs 2.6Hz processor. Am I missing
I made a similar switch last August. I was running FCP 6 on a MacBook Pro 2007 Intel Core 2 Duo with 8GB RAM. I'm now running FCP X on a Macbook Pro 2.6 Ghz Intel Core i7 Retina and it's much faster. Running off the Flash hard drive is a significant improvement over my old laptop. I usually run my media from a 2TB Western Digital 3.0 5400 RPM external drive, it's still pretty fast (but not as fast as running from the flash HD). Though really, it's not a huge difference.
Switching from FCP 6 to FCPX has been a huge change there. There were a lot of options and controls removed, so depending on how much control you are use to having you may find it a bit frustrating.