On the spurs, they will cost about $30. It becomes exhorbitant if they wear out or continuously strip, but assuming they have a long life it's not a big deal to cough up the extra cost. Given 7mm face contact width, acetal resin material, and hopefully no undercutting from the pinion, I am banking on them lasting a long time. If they don't I will need to rethink my design!! :)

I have considered the 51T Ofna spur. There are a couple troubles with it. First there are no published measurements of it regarding the spacing and size of its mounting holes and they're not a stock item in car hobby shops here for me to go look at. I plan to use the stock 48T spur as an adapter plate which leaves only a few mm of tolerance for drilling extra mounting holes without sacrificing strength - the 51T might be too small and too thin around its outside for mounting like this, and its small size would probably require me to machine away the teeth of the stock spur so that they don't get in the way - with a 56T spur I can leave them behind and just drill 4 mounting holes. At 51T my low speed gearing options will be limited until the motor case touches the drive shafts. It will also mean using smaller pinions which exceed a pressure angle of 20 degrees.

With my intended pinion range of 16-24T I can gear for 30MPH to 50MPH. With a 16T there will be about 3-4mm of clearance between the motor case and the drive shaft, which leaves me with some breath room to add a cap to the front of the motor to seal its big holes.

The 1912 is the same power rating as the 1512 but is 2 oz. heavier. I have considered the 1910 to save weight, but it would have a big drop in max power and from what I've read 2000+W seems to be what you need in a 1:8 buggy?

The packs will add 500g of weight. I got the impression that 4S 8000 MAh was common in buggies, and those weigh 725g...

The really nice thing with the maxamps 2100 cells is that they are only 100mm in length. That will let them mount very nicely in my chassis without them pushing up onto the dust guards. I will post a diagram of my planned component layout a bit later...

Thanks for your input!