It gets old explaining that higher C ratings does not mean it can push more, it means the system can draw more from the battery. Just like a car battery. Your car doesn't PUSH 675 amps to the starter, the starter draws that amperage. If batteries "pushed" amps electrical systems would be a whole lot more complex. 1/8 scale brushless system draw heaps of current, 1/10 not nearly as much. You'll know if you're drawing more than your batteries can deliver because they'll either get really hot or go poof.. or both. Your ESC could also shutdown if it cannot get enough current, not really a problem often but it can happen. Get the highest C rating you can afford, as higher C ratings also means higher quality lipo cells (usually, not always).