My take on your question, the Sirrus you have is a beautiful bike that is more than capable of meeting your needs, it's basically a flat bar road bike with the added ability to do some gravel work if you wanted to try it due to the larger tires. It already has a higher end Shimano drivetrain, hydraulic disc brakes and a top of the line aluminum frame with a carbon fork and a built in shock absorbing system in the head tube.
The only thing your looking for is a very minor increase in speed? It simply isn't worth making a change. If it was me and the incremental increase was that important, and I had the cash, I'd simply buy another bike that was a road bike.