Default [Q] How to speed up

Hi guys,

hope somone has some tips for me.
I running my desire Z with CM7 (ILWT ROM) since one year, and i'm pleased so far.
But now from time to time the device will become slower.
One thing i do is delete cach+dalvik, then it is faster for a while.

I overclocked to 368 -> 1113 conservative to save battery.

I saw there is also a cache directory in /data oder /system, what is that for?

Im waiting for a new rom with KitKat for the DZ, hopefully there will be one, but so long i appreciate any tips to make it faster.

Thanks in advance