For racing I would recommend packs closer to 5000mah, to keep the weight down. Since you are looking at the turnigy batteries, have a look at the hobbyking site
http://www.hobbyking.com/hobbyking/store/index.asp
These are popular choices, I linked the ones in the UK warehouse assuming you are located there.
Full sized pack
http://www.hobbyking.com/hobbyking/s...arehouse_.html
Shorty pack
http://www.hobbyking.com/hobbyking/s...arehouse_.html