I would look for something with curved ends like the Hirsch Mobile or Hirsch Principe Leonardo if you want leather. The reason I recommend the curved end strap for the Sport Evo is simple. The case is so thick, non curved end straps just don't look quite right. Here's what I mean...
I took a Hirsch carbon fiber and dyed the white stitching red with a sharpie so it sort of resembled the GO Trieste strap. From head on, it looks OK, but from an angle it isn't quite right with the straight ends as you see, due to the thick case. I don't know though, maybe you like it.