Like I said before, you might buy just one and give it a test drive before you invest in the whole amount for a sweater. The numbers you've run are an indication of what to expect. The gauge given should work in most worsted weight yarns IME but of course YMMV substantially.
ETA Do you have any worsted weight yarn on hand? You could knit a few coasters with garter or seed stitch borders and the middle in stockinette to get an idea of your gauge with different needle sizes. Any worsted weight yarn would do as you'd just be going for ballpark numbers.
I should never overestimate my basic arithmetic skills.