+1 for trying synaptics(4). It uses wsmouse "absolute mode" (covered by wsmouse(4)) and has a lot of Options (more than ws(4) which is used by default), some of them may help. Check log file then, you should see "synaptics" driver there.
You can also try to stop wsmoused(8) before launching X. Although its man page says it should coexist with X (at least when wsmouse is used) But if your USB mouse also has troubles, it could also be accel. issue: You may try to play with "xinput --set-ptr-feedback " or "xset m"
