Just looking at SI's site again... The SLK is 145 mm, SLR is 155. The SLR is also 8 mm longer. The cut-outs are very different (from the pictures, much wider on the SLR, but both are biased toward the rear).

Again just going by the pictures... the SLR appears to be more T-shaped, but on closer inspection, it could just be that the rear is wider and the nose is about the same width.

Poking around their site brought me to the Turbomatic. Apparently they just re-introduced this classic last year, now with cut-out. 153 mm, reasonably generous cut-out, and verrry T-shaped. I'm seriously tempted.