i wear a one piece on the track and occasionally on the street as well.. i don't like how the two pieces tend to bunch at the joint between pants and jacket.
I have a 1pc and ride street only. Like you, I also have a good jacket, so I didn't see the point in getting a 2pc. Yeah it sucks when you have to take a piss (or worse), but I've done both so it can be done.
I have both and like both. Street is always going to push toward a 2 piece because you can take half off and your pants don't fall down. Track 1 piece gumby suit is safer. No chance of a zipper failng and you getting rashed or twisted up in 2 pieces. But a 2 piece track suit lets me get my back protector on wthout help.
To make the decision a little easier a lot of track days require a full
wrap around zipper. So I would say forget about the partial ones. If it were me I would buy a one piece but I do have a 2 piece suit right now and I have been happy with it.