how many daily unique visitors to a "free tube" to generate $4000 a day
 

Obviously there is not one set threshold but approximately what would it take. I know there are tons of variables but a generic non niche tube site with say 500k uniques a day.will that bring in $4k?

If your getting $2 cpm thats $1000 then there's affiliate links, premium upgrades n other income streams

You wouldn't know unless you give it a try and get a few sales. It all depends on your offers (rev share/PPS) and marketing strategy. Once you get those numbers in then you can figure out how to scale it up. Stop doing what isn't working and do more of whats working.