The less resistance the more punch the battery will have. IR is directly related to the C rating. The problem is. Most if these lipo companies are a bunch of bs'ers. So far my SMC's have the best IR but I feel my BMI's have a better track feel. End voltage after s run is also better on my BMI's then the SMC's.
If your in the market for a couple great batteries you can't really go wrong with either a BMI or SMC.
www.bmiracing.com
www.SMC-racing.net
Roger