Does it do it after a new reboot (and pull battery)?

If it does, you have a different problem. Also, OC did quite a lot for me, you should consider upping to an 800 or 900 MHz, that alleviates the unresponsive phone UI thing.

If you are willing to take a risk (might be time for a reflash if you scr* it up), then take my path:

* Install Titan's power kernel
* kernel-config load ideal (as root)
* kernel-config limits 250 900 (as root)
* swappiness > 10 *see above for command line)

This alleviated much of my issue, up to a point where (if I keep up with my 48-hour reboots) I don't get ANY dropped call/missed call due to stuttering.

Also, if you want to fix the audio stuttering there's a patched pulseaudio in this forum. It has its own drawbacks, like the ringtones randomly reverting to default (Rings like Nokia Tune for no apparent reason).

If you are willing to take that, then PulseAudio fixes that annoying stuttering when picking up calls and while playing audio.

There are partial fixes all around you. Give theose a try and we'll see from there. I have other suggestions.

Right now I run with Kernel, OC, PulseAudio and swap, plus a few slight mods that help me get by, like relocating stuff to my faster external card.