Touring specific bikes have about 460 mm chainstays for a 58 cm frame. The bike I use a lot is a Bianchi Volpe, a CX bike, 57 mm frame. It has 416 mm chainstays, about 1.75" shorter than the touring specific bikes. I use Ortlieb Back Roller Classics on a Tubus cargo rack. I have size 10 feet, and just barely clear the the panniers on the 416 mm chainstays. I'm not sure why you are having heel strike issues; your bike's chainstays are only about 3/4" shorter than most touring bikes.