I wasn't sure, and bought a week ago today. I bought the SG Sport since it was cheapest to see how I liked it. I love the watch, but not a fan of the all blacked out look, so going to take it back and get a regular SS with the black leather classic band (found a good deal on eBay, with AppleCare) and will pick up the sport band to use for workouts and yard work.
One correction to your post... its Space "Black" SS, not Space Grey. The SG is aluminum and the sport.
My wrists are relatively thin and the 42mm sport band that comes mounted I am on the 3rd hole from smallest and its snug.