Can a Tri bike work for me?

I am a 50 year old male training for my fifth triathlon season. I have done mostly short course races to date but I did finish my first 70.3 this past summer. When I bought my bike I thought triathlon would be an occasional diversion. I am riding a Felt Z frame with clip on aero bars and a Cobb saddle. I am now very committed to the sport and my goals are getting loftier so naturally I am considering the benefits of a Tri bike.

I have a chronic physical issue that makes it imperative that I keep my weight on my sit bones. My current set up and fit allow me to do that. I stay in aero almost all the time, no matter how long the ride, and am very comfortable. My questions for the group:

1. Is it realistic to think I can get into a reasonably aggressive position on a tri bike (ie, enough to give me an advantage over my road bike/clip on) while still keeping my weight on my sit bones?

2. How much improvement can I expect to gain, given my constraint?