A rod rated 40 (50) 60 is what the manufacture calls a 50 pound rod. It should be able to be max-ed or pushed to a 60 pound rod. That means 60 pound rated line. The low end of 40 means that anything less than 40 pound test will not give the rod a proper load. Since this rod is designed to be a 50 pound class rod, you probably should not have more than 18 pounds of constant drag used on it. You should also use a minimum of 13 pounds of drag to get the full advantage of the design. It should be able to lift 17 pounds of dead weight with no problem.
The better blank manufactures are conservative on their ratings. That's why people push them beyond the rated strength.
If you don't want to snap the example rod above. Start with 15 pounds and add one pound at a time. When you feel you are "High" sticking it and you feel it starting to twist, you have peeked out. Use a gimbal to keep the rod from twisting during the testing. When you start hearing cracking sounds, stop. The glass is being compressed on the under side, and stretched on the top side.
The Bar-Bar 30-50 that starts this thread is really a 40 pound rod. A 14 pound dead lift should be most this rod can fish. Ronnie pushed the rod by 40% of its rating. I'm surprised he wasn't holding two pieces. It should be fished with a 13-15 pound drag setting.
One more note. Don't start bouncing the weight after you have raised the weight. You will hear the dreaded firecracker sound and be holding two pieces. Just do a slow controlled lift and slowly let it down.