Only during editing.
A small anecdote:
We once shot a TV pilot, were we recorded the footage as 1080i/25fps video using an MPEG-2 codec (XDCam), we shot with two cameras, and then we had to synch both cameras (multi-cam project), thus the editor could choose the angle himself.
We had a Mac Pro 3,1 with two quad core CPUs using Avid Media Composer (4 or 5, though it didn't use multiple cores, which invalidates the anecdote for this purpose I guess) and we didn't transcode the footage, only rewrapped it, due to time constraints, thus the playback one stream was okay, but as soon as we wanted to play back two streams at the same time, it would take a second to actually play after hitting play.
As one hits play a lot during editing, it was noticeable and frustrating.
An older G5 PowerMac was able to play up to eight SD streams back at the same time, but those SD streams were properly transcoded.
Now with FCP X being capable of using multiple cores and threads, and your MBP having a 4-core CPU and 8 threads, you might not notice anything.
If you properly export the finished sequence for whatever application you use next, it will play properly on any display device it is meant for.