Given how much you've played, being able to look at the Terran's base when he has no barracks building and decide whether he has cut SCVs is something you should be able to do intuitively...of course you could take the time to learn the exact # of SCVs he should have at what point, but that takes time and is risky. What always ****s me up is when he does the eco 2rax (cutting no SCVs) where the second one is somewhat proxied.
There's a huge difference in what the Terran has going CC first vs going proxy 11/11. I just tested this out on Bel'Shir. If you scout at 13, you'll reasonably get into the Terran's main (and be able to see what's going on) at around 2:40.
FWIW, around 2:25 is when I had 400 minerals to build my 15 cc on the low ground. This is what my mineral line looked like at 2:40 (when the Zerg is presumably scouting my base):
http://imgur.com/znxkeNC
This is what my mineral line looked like at the same time, when I was going 11/11:
http://imgur.com/t1wGzTh
You see the difference, right? Just look at how many SCVs are paired in the first vs the second example. Even if that doesn't work, this scouting timing is right after you've put down your hatch and before you get your pool- just spend a second or two counting, while making drones using hotkeys.