Borgata actually experimented when they first started spreading NL. It was 10% to $4, then they switched to $5 per half time charge then went back to 10% to $4 rake. I think that the rake is fair. The time isn't that bad (that was NYC club standard) But the max buy ins in both cases are $250 to $500 depending on where. The $5 time charge only becomes insane with a $100 max buy. If the same group plays for a few hours all of the money disappears.

For low-limit rake games I think 10% to $4 is fair (AC standard up to 6-12, 10-20 and up is time). $6 max is definitely a lot.