I ran 14ga wire in my T4 with an orion R10 and a 6.5 motor doing 20 minute race runs on a track all summer long, b/c that's what I had. I'm going to assume with the 17.5, you're going to time and/or gear the crap out of it. I doubt you'll save enough weight to make much difference, and 12ga wire will help things run cooler. Up to you though, as I said I've run it that way without problems, but currently running 12ga.