If you have freezes like that, then you did something wrong while flashing: No full whipe including internal sd!
Android 4.x has a new, dynamic memory allocation system, less free ram doesn't mean slower phone. It will dynamically use the occupied memory and backgrounded apps just "virtually" use that memory, but release it as soon as some active programs are in need of memory. So don't get tricked by a small amount of free ram on Android!! And please don't use the task-killer function in MIUI or with other task-killer apps. This is contraproductive, since it will restart internal services and produce zombie tasks which use more memory. Just let Android handle your memory allocation and don't care about it, since the N7100 has a LOT of ram.
If you experience lags or freezes, then something is NOT good with your installation, since MIUI 3.2.22 is stable for N7100 users, and thousands of users can't be wrong. No particular bugs known.