You can go up in mah, but it's not a free lunch. The more capacity you have the more the battery weighs. The heavier the plane the more throttle you wind up using, not to mention your plane may not fly as well. You also will change the CG which may require adding weight to fix if you can't shift your battery around. If you liked the way it flew with a 2600 it won't hurt a thing to go that route, but understand that adding 20% more battery capacity doesn't mean 20% more flying time due to needing more power to fly the plane.