Thanks for mentioning me. There's a guy Cliff Wilson who won a natty pro card at 160-something at like 6 feet and change, if I recall correctly. The guy is VERY dedicated and although he has some strengths and good condition, some think he came in too stringy and looked like a professional dieter rather than a pro BBer. But as far as BB I respect him a lot because he is dedicated and busted his ass. So you never know what hat will happen in what contest, but obviously you prefer to have some mass.
As far as knowing when you're ready, I don't want to sound silly or open ended, but you'll know when you look like a BBer! It's the same concept regarding fat. Like when people ask what bf percentage one should be, it's really as simple as looking in a mirror. If someone looks fat, they are too fat. And when someone looks like a BBer, they're ready.
Go up to an experienced BBer and ask him if you're ready or how much work you need. That's the best thing you can do for your inquiry. As much as forums like TN are great, they cannot substitute socializing with other BBers. It just can't. My friend Josh got his ANBF pro card this past Saturday. When I met him in the gym last year, he had no idea what to do. I told him, "look, I'll introduce you to my friends and you will learn how to go about this." Months later he dieted, learned the poses, and got on a stage.
When I got ready for my show, I'd travel to the Mecca of the East, Bev Francis Powerhouse, for some of my workouts. Why? Because I thought that although I'm not a top IFBB pro, I want to be on "the inside", and although I'm not Dorian Yates, I wanted to be the most psycho BBer that I could be personally. And if I was the lowliest BBer l in the whole gym, so be it! I'd rather be a lowly natty BBer at Bev's than a decent BBer in a gym with no BBers at all.
You know what I'm saying? If you want to compete you need to hang with competitors. They'll let you know what's up and how to go about it. You might have to hire one too for your first prep as well.