try newer builds. those perform very well, when phone app is cached it also opens immediately, otherwise it takes perhaps 1 sec. greenify helps a lot to prevent other apps from slowing down your phone... what is the main culprit, because ICS/JB needs more RAM than GB... where this also can happen with lots of apps open.
when you don't need BT i recommend cm10.1, the latest build from 07-09 is blazing fast! not comparable with older builds from 2012... that indeed have been kind of slow in certain situations...
The last build I used was CM10 3.07.2013. I tried them all, doesn't really make a difference. I greenify the s*** out of my phone, always. But you can't do anything about the OS that is slowing down the phone. The newer the androidversion is, the more weight it puts on the hardware. Makes sense when you take the rapid development of the androidphones into account. We have quadcorephones now with 2gb ram, and the current OS is build with these phones in mind. Don't now about CM10.2 but I red it needs even more ram than previous CMs, so I really don't see, how this could be any better. I don't care how "snappy" I can scroll between homescrees. My phone has to be fast at opening apps. The more memory there is to do that, the better.