You would need to purchase the Castle Link interface, which is a cable that has a USB connector on one end, some electronics in the middle and another connector that attaches to the receiver lead on the Sidewinder ESC. The software you download from Castle Creations and run on a PC. If you can't use Castle Link you can still adjust ESC settings through your transmitter.

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If you've got 6-8 cell NiMH packs (or even if you had 2S LiPo) then the 5700 will be faster on those batteries.

However if you came across a 3S LiPo you are not supposed to run that with the Sidewinder/5700 because it exceeds the specs of that combo. You can run the Sidewinder/4600 on 3S LiPo and that will be faster than the 5700 on 2S LiPo.

This of course just takes speed and budget into consideration. I don't know how these two motors feel and compare around big and small race tracks.