I'm a new FCPX/Motion5 user (as of 7 months ago) and my current Mac is an '2011 MBP 17" with 8GB ram and a 500GB SSD and I'm still on Lion (I don't remember which quad-core processor I have...and I'm not on the MBP right now to verify). At any rate, I've recently done some work for hire that is very closely related to what you are talking about by way of a series of guitar demo videos for Vibrance Guitars. I used multiple camera angles for certain segments (everything from GoPro cams on headstocks to cheap webbie cams to a nicer Sony HD video cam to a Nikon D7000 DSLR camera). The biggest issue I've run into with this set-up has been when ingesting new footage from SD cards into FCPX...the importing process isn't too bad but the rendering and transcoding takes quite a while, and so much of my time (while filming) was spent waiting on FCPX to finish analyzing new footage.
Also, I use an external Lacie RAID drive (2x 3TB 7200 HD's) with Thunderbolt to host all of the video footage and I just stream directly from that external drive when editing and honestly it seems like the Thunderbolt keeps the pace just fine and doesn't factor in as far as any lag goes. That being said, I do usually have to wait a few seconds whenever I add any sort of transition effects, color adjustments, or any other clip-related edits within FCPX...it's definitely not an instant rendering...but it isn't bad either. But the editing work is definitely workable with these specs/set-up. That being said, I can't help but think that having an SSD is a big benefit to the whole editing process, and it especially helps whenever I need to transfer large amounts of data back and forth between the Lacie and the MBP's internal...a 100GB transfer typically takes 90 secs or so. It's crazy fast and it spoils you pretty quick.
On the other hand, when working in Motion 5 it seems like there is a complete different set of issues, namely the MBP's built-in graphics card struggles with any sort of intensive graphics rendering. To support the Vibrance demo videos I contacted all of our pedal, amp, mic, interface, etc manufacturers and got permissions to use their logos, mention their names in our equipment credits, and make vector animations of the gear we used. So then I bought Motion 5 and learned how to make graphics/animations, at which point I started designing the pedals, the amps, mics, the interfaces, etc, all with moving knobs, tubes that light up, LED's that dance as if being fed with signals, power lights that turn on/off, switches that can be flipped, etc.. In the course of doing all of that I started noticing serious lag issues when trying to play back my animation sequences in real time and so it made a lot of the editing a bit trickier, to wit I've had to guess on a lot of the edits, render out a test video to check how the edits looked, then go back in to make small adjustments again, etc., over and over until I got things to my liking. So the real issue here has been the lack of horsepower in the MBP's graphics card. So if you plan on doing a lot of graphics stuff (as a front end to FCPX or whatever), you may need to mentally prepare for challenges there when it comes to playback within Motion 5 itself. That being said, Motion 5 is a great piece of kit and for somebody like me who hadn't done any graphics or video work until 7 months ago, it has been very accessible and it has been fairly easy to get my head around. I'll link one of the Vibrance demos below to give you an idea of what sort of work I've been using FCPX for. The equipment animations won't be featured in a video until after the main guitar demos are finished, but I can PM you a link to a privately hosted video example of the Motion 5 stuff if you like (I sent out a forum friend request to facilitate this). Here's a link:
http://youtu.be/GzkOHk6-HCc
Hope this has been helpful!
