You may not need more volume, but you'd certainly notice the jump in quality more power will deliver. You can never have too much, but you don't need to use it.
I would imagine the MS 309 to be a solid upgrade over the Gale. At the same volume it will give less distortion, go deeper and with it's notch filter, you can sort out the worst peak in it's frequency response. You'd be amazed how much difference that makes.
Russell