Gearing help

[mothman]

Im almost done collecting most of the parts for my BL savage. Going to order the BL stuffs along with the pinion from Mike as soon as the wanderer come in.

Ok here is my 1st question, Im not sure what gearing setup should I use. I know Serum has the Excel speed calculator but since Im not sure about the gear ratio of the UE 8 spyder diffs that I bought, it would be extremely great if you guys can help me on this. By the way, Im looking to get around 40mph and Im using LOSI LST tires (7"X4").

Secondly, I was planning to use 7XL but after reading a thread in this forum, I think I might go 8XL. I have 5s Lipo by the way. Im not really looking for speed, runtime is more important to me. Ive read that 8XL can give me more runtime. SO what do you guys think? Please shed some light..