This is the first I've heard of thrusting with a 3.5lb staff. Where did you get the staff and what is it made of?
mine is made of hickory, I think, and I ordered it out of a martial arts catalog 10 years ago. I believe it was century's martial arts catalog, but they don't seem to have anything comparable anymore.
I ordered a couple here for friends which are ~3lbs for a 6 footer and ~4 for an 8 footer. they come unvarnished, though i guess you could shellac them and add a little bit of weight.