just re-read your post....you already use it
I have just a single dock with 16 icons on. 2 of which are to apps (Firefox/Thunderbird), 3 are to a docklet that does Shutdown, Standby and reboot. 3 are folder shortcuts with the remaining 8 being stack doclets with each 'stack' having between 3 and 24 links inside.
I can't say that they've ever lagged to the extent you are seeing.
If it helps these are my settings



My Dock
