Hello,
I believe the '59 Roundback profile offered by Warmoth is *nearly* identical to the current Gibson SG line. I have a '94 Les Paul Studio with the exact specs of the '59 Roundback profile, which is what Gibson usually refers to as the "rounded" or "50's Rounded" neck. I've been looking into a Warmoth SG and have thought the same thing so, I looked up the stats on the Gibson site. The 60's Slim Taper would be a fraction thinner--I imagine closer to the Standard Thin as the rest are saying. Looks like the SRV & Wolfgang are close to the same thickness as well, albeit with the asymmetrical contour. The Fatback and Boatneck would be a bit thicker than the Gibson rounded neck looks like to me. We are talking fractions of an inch here though...
I think it all depends on the shape of your hand and what you are comfortable with from your experience. I personally get very fatigued by thinner necks (i.e. Ibanez Wizard) and have found my Les Paul to be perfect for long nights onstage--little to no fatigue. I have smaller hands, so who knows. I have an American Strat with the "C" shape I love to play as well, though it does start to fatigue my hand after several hours. Part of that I think is the angle the guitar sits on the body as well. Les Pauls and SG's are easier to hold at an upright angle and the neck is angled back toward you so that helps also, whereas the Strat is straight and pointed down and away from the body (in my case).
So, perhaps the shape of your body and hands are something to consider. But in my own experience, I do like both the '59 Roundback thickness and the Fender "C" quite well, as do most people. Those are the two most commonly appreciated back shapes from what I've heard. I'm sure the Big 2 did some degree of research and arrived at those shapes based on lots of trial and error. The 2 most popular guitars of all time can't be all wrong! I'm sure Warmoth did their homework as well. I think you are safe with the Standard Thin for the most part.
Hope that helps.
Good luck with the SG--post pics when you get it done!