Go lighter is good cept that the c of g is affected. I have the same acft, motor and speedy. I tried a Kokam LiPo 1500 and 2000 and the thing went like a caned cat but the balance was all wrong. I now run 2 x Kokam 1500's. Squeezed right up against the front bulkhead. I am using a 6.5x4 graupner scale prop. The thing howls. You want vertical performance you will have it with this set-up. Weight is not so much of a problem when u have horsepower. Appch speed is a little higher but................ Be careful with control surface throws too. It is VERY sensitive. If you do go the Lipos just make sure the cutoff is set from the default 5v to 7.6v (I think) for 3 x LiPo cells. [>:] Let me know How you go.