Play back is sticking and freezing up a little bit. I changed the viewing quality between both selections, does not seem to matter which one, since both stick. I am no using an external hard drive. The only thin I have open is my firefox web browser. Stats below on my system is below. I am operating final cut pro x.2.
2.8 GHz Intel Core i5
8 GB 1867 MHz DDR3
l Iris Pro Graphics 6200 1536 MB
Depends on the codec of the footage, the number of tracks you are playing back, the capabilities of your hard drive(s) and whether you have optimized or original footage and are viewing in proxy or original quality settings. In short, kinda depends.
I experienced this and it was fixed by closing the information panel. This prevents the need for FCPX to load the information of the new clip into the panel every time you move around the playhead which causes an almost imperceptible delay but can make the playhead feel "Sticky".