my first choice would be the sierra 80gr sspb, followed by the 80gr hornady ssp. if ya can find em, as sierra has quit makin the single shot bullets as far as i know.
....also the speer 80gr bullet would make a good choice, from everything i've heard on it.
the 80gr nosler balistic tip should be a good one, but i can't remember any reports on it in 6mm handguns, other than good accuracy. :?