You can do that yourself knowing the weights of the two batteries in question and itís mounted CG position relative to datum. If mounted in the same place, your empty CG will move aft slightly if mounted forward, and the opposite if mounted in the back. Youíll be able to carry about an extra 2 gallons of gas at the same gross weight with the EarthX.
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015