Absolutely! MaximumPC oc'ed a GeForce4:TI4200 to almost TI4600 levels and oc'ed a TI4400 faster than a TI4600. Just clock up by increments of 5MHz and run that for awhile. If its stable go up another 5MHz and so on.
You'll know when you hit your limit when games crash hard quickly and/or you begin seeing visual artifacts on screen all over the place.