[buster73]

Unless you are serious about track results you won't see a big benefit in daily driving or for DE events. Installing a smaller battery closer to the CG will of course reduce overall weigth, move the balance further back and reduce inertia. Without any other modfications this will not necessarily make you faster as it migth increase understeering in slow corners and make the car more nervous at the limit (though this can be fun on the track).

I just installed two Odyssey batteries in my 73 (original location) after my old batteries died. For track events I can take out one of them, but I don't really expect to see a significant difference. The car is still much faster than the driver.