I bought the cells from here:
http://rcbuy.vstore.ca/product_info..../cName/lifepo4
I was wrong about how much balast I needed to add! My 4600's pack weigh 300g. These packs weight only 175g. That is a 125g difference, so I added another 40g stick to the already 80g of balast. I would have worked on a setup for the lower weight, but I did not want to alter my setup. Adding weight was a simple fix. I would like to rebuild my CRC 6-cell car and run that with 6-cells. Why add weight if it is making you faster or last longer?
Just from what I noticed, these cells on 17.5 Motors would be close to the same lap speeds as 13.5 motors.