Gearing help

I want to run 8S. I need to decide between a 1512/2Y or 1912/1Y. I do not know which yet as I still need to see how much space and gearing I have to work with in the buggy.

Upsides of the 1512 are that it's easier to seal and is 2 ounces lighter. Upsides of the 1912 are that gearing options are easy due to lower Kv.

I would like to be able to gear my car for top speeds of 40 mph or less (even though I will probably experiment with faster too).

From specs I've read, 1:8 tires are approx 5 inches diameter.

Open to 8S suggestions though. :) I have not purchased any of the power system components yet.