Track your winnings. If there is a hand count, take a note at what count you started and where you finished, and how much you won/lost.


Some things don't add up for me here:

I can play twice as many cash tables as sng's. I don't understand why the opposite is true for you.
Hand selection is usually WIDER in cash games than it is in sng's - at least according to stacks as you're not worried about ICM in a ring game. +relative stacks are deeper pretty much all the time.
Don't go for a specific winrate. Just go for whatever is best in terms of money divided by time.