GOT IT! (well for me^^)

first i reflashed and set up my phone from the beginning (only restore of contacts/communication, nothing else). i installed my usual stuff (i.e. cssu (testing), kp v49, maxcpu- but not speedpatch or anything "patchy").
it lagged again, so i thought about kp v49 being the cause and bricked my device (don't say anything )

then i started like i did above again with a complete clean device and there was this lag again when unlocking the phone (i.e. 5secs to start phone from desktop).
things i did install this time:
- cssu (testing)
- kp v42 (from extras repo)
- maxcpu
- conky
again that lag.

uninstalled kp and maxcpu, reboot - no lag.

then i installed kp v49, reboot - no lag.

maxcpu installed: there you go again - lag! (of course rebooted) and completely without even touching the widget!

uninstallation and reboot: no lag at all.

so for me, maxcpu caused the lags.

btw: is there any other solution to overclock the device in an user-friendly way (=via gui)?