From the looks of it your motors can draw 15 amps max. So I wouldn't recommend going any bigger on the props. If you feel like you need more stability or battery life you can try a 10x4.
10x4 / 1040 (Same thing to answer your question) : This will require your motors to spin faster for the same amount of thrust, BUT since the props are spinning faster it will give you more kinetic energy and help you be just a tiny bit more stable and give you a bit more battery efficiency.
There are a LOT of different props out there you can try. Even using the same prop by a different company can give you different results. Based on the weight of each prop and the surface of each blade can effect your flying.
You can probably even try something like this...
http://www.hobbyking.com/hobbyking/...Blade_Propeller_8x4_5_Black_CW_CCW_2pcs_.html
I hope this helped at least a little.