The curl has been a test for arm strength since forever. The current world record holder is CT Fletcher. He curled 225 pounds and here is the video:
Start watching at 4:35.
There are some other strict curl record videos but they are actually cheat curls, I don't know how they pass them. Like this one for example:
Strength athletes today rarely take the curl seriously but the athletes of the past did. Names such as Dough Hepburn, John Davis, Herman Görner and so on excelled at the curl. Though there isn't valid evidence for their curling feats of strength, judging by their other lifts if they took the curl as seriously they must have lifted big poundages. I doubt their claims were true as I don't think that Hepburn curled 250+ pounds in a strict fashion like I outlined at the start of this post, nevertheless he had incredible arm and overall strength.
A guy at the gym I train at was telling me how he can curl 30kg dumbbells for reps in a STRICT fashion. I called it bullshit and loaded a mere 50kg(110 pounds) on a straight barbell, did a strict repetition with it in order to demonstrate to him what strict means and told him to do the same. He failed and started making excuses how it's bad for the joints etc etc. So if someone claims outrageous curl numbers make them curl in a strict fashion like this and prove them wrong.
I don't have a set advice on how to train the curl, it depends on your goals and how you are willing to train it. Remember there are many ways to skin a cat. I, personally, combine low with high reps and the sets vary depending on how much I'm willing to push myself that day, how rested I am and other factors. I plan on setting new strict curl PR soon as I've been hitting dem gunz hard lately.
Görner was a friggin beast for his time