More likely an indication of slow hard drive(s) and/or the type of video file that requires a fast i7 for smooth playback
But... More information needed for someone to help... please click these links and provide the requested information
-Information FAQ http://forums.adobe.com/message/4200840
-Effective questions http://forums.adobe.com/thread/416679
-How to get help quickly http://forums.adobe.com/thread/419406
What are you editing, and does your project match your video?
Please NOTE that the PPro CS6 screen may look a bit different (I use CS5)
For CS5 and later, the easy way to insure that your video and your project match
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/thread/872666
-and a FAQ on sequence setting http://forums.adobe.com/message/3804341
When your project sequence is correct, you will not see a red line over your timeline at first import, before you do anything to the video
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing
Is the lag only in your timeline / program monitor,
or in your source monitor as well?
Has CS6 ever functioned properly?
If so, what has changed in the interim?
Do you see the same playback problems
when viewing both SD and HD media?
Are you sure your GPU driver is up to date?
Switching from a GT 620 to a GTX 650 Ti
would not be likely to fix your problem.