The reason for the xe2x80x9cstutteringxe2x80x9d could be a combination of different factors.
First is of course your computerxe2x80x99s power and video card. The more power you have, the more the number of FPSs your computer can xe2x80x9crecordxe2x80x9d.
Despite that, QuickTime is not known for its xe2x80x9cfastxe2x80x9d recording, so I suggest you give a try to different alternatives. This comparison is a little bit xe2x80x9coutdatedxe2x80x9d because some (if not most) of the applications mentioned have been updated and have fixed or changed some of the problems they had, however, it should be a starting point for your final QUickTime Replacement. This other link has a very similar list, but rather than a review is a list with a short description of the products.
For reference, the most important Screen Capture tools for OS X (or to put it in another way, the xe2x80x9cmost used onesxe2x80x9d) are (in no particular order): iShowU, Snapz Pro X, ScreenFlow and one that is missing from those lists (because itxe2x80x99s a new player in the Mac world): Camtasia for Mac (which Ixe2x80x99ve been betatesting and itxe2x80x99s quite good and in par with the ones Ixe2x80x99ve mentioned). Some features missing from Camtasia 1.0 have been addressed in an update and I know they are working on a newer version after getting tons of feedback in the Beta forums (which I canxe2x80x99t disclose because I participated).
Ixe2x80x99ve personally tried those four Ixe2x80x99ve mentioned (i have a Snapz Pro license) and I think they more or less are the same, but some were (when I tried them) faster than others but lacked certain features. All in all, the xe2x80x9cbestxe2x80x9d doesnxe2x80x99t exist, they all have strengths and weaknesses so your best bet is to give them a try and see if one does the job.
Last but not least, remember that quality also plays an important factor in CPU overhead when recording, try to keep your CPU load low and reduce the recording quality as much as you can afford.