to be honest there really isnt such a thing as a 'general' ratio to lump all of the conversions together for the pure reason that every paysite gets different sources of traffic from different locations globally
however as you have said i think the consesus around here would be that sites with exclusive content with multiple updates will convert and retain better than than the standard filler shite most paysites have in them
the best thing to look at is your btm line $$$ if you are making money and are happy with what you are making and it sounds like you are then keep on doing what you are doing changing something can do one of two things..
improve something or fuck things up completely lol