WHICH GWS Formosa do you have?

The "Slope Glider"? ( Formosa II ? )

Or the small Park Flyer EP?

I would guess that you have the Formosa II as that battery would probably be too big for the Parkflyer...

The Rimfire and Battery would seem to be too big for the Estarter.

If power was an issue with the stock brushed motor, you might want to consider using a smaller ~1300mAh LiPo battery with the brushed setup.

You may need to change out the ESC if the one you have does not support LiPo's but many do... e.g. the Electrifly Brushed ESC's support LiPo's by moving the berg jumper.

This would increase the voltage resulting in more power, while upping the run time. Since LiPo's are lighter, it would not overload the plane as well.