which version of premier cs/5/6/cc? are you using and have you been watching activity monitor, a lost of the time a lack of smoothness is slow media that your playing files from.
Ie the internal drive your media is on is starting to get full or fragmented.
do you have a dedicated cache drive?
+rawweb is correct
cuda dose a lot less than then hype around it makes you think, a lost less.
& even in CS6 openCL is a thing
http://blogs.adobe.com/premierepro/2012/05/opencl-and-premiere-pro-cs6.html
(wow FCPX is fast in your tests, im going to have to try the demo agen been ages miss read the stabilize numbers as smily faces as the numbers where so low saw the :5 as a :S at first
)