Stars 18-man's: When to move up?

[QuattroFour4]

I've been playing the Stars $6.50 18-mans for a little while now, about 1,000 of them, and I've made about $1,200 profit, so (correct me if I'm doing the math incorrectly), I make an average of $1.2 profit, so that gives me an ROI of 1.2/6.5=18%. I'm pretty sure I have the skill to perform at the $16 18-mans, but I doubt I'm properly rolled for it. What should my BR be at if I was to play 1/2 $6.50's and 1/2 $16's and why? Thanks.