I too have both, my STI has been highly modified and is basically only a STI slide frame with a few of thier small parts. When I picked up the PM9, the only mods were adding grips and magwell, then lightly breaking the edges on the back of the thumb safety lever, lightening the factory trigger a little. In the end, both are similar, but I have far more $ into the STI so it is easy to say just go with a PM9. DW's are fit tigher and have better lockup too, so it will last longer.