You can put more watts into it for sure, and increasing pitch is one way to do it. However, you should really be asking yourself whether that is the right approach, increasing pitch will only make it fly faster, for less time. If speed is what you want ( and why, when this is only a trainer ? ) then fine. If however you want climnb and thrust then more watts via more pitch will not give it you. If as you say, you are inputting 110 watts, from a 3s Lipo then thats a current of around 10.5A, and your battery is only really good to about 13A ( at 10C which is about right for a 15c battery ). Sure your ESC is plenty big enough, and your motor is good for maximum 35A and a constant of around 20 25A, but it is a fairly low Kv motor, designed to swing large props.  As Eric says, be careful as you start increasing props ( pitch or diameter ) as this will increase current a lot - as will going up to more cells. This model was designed around basic brushed stuff, and an 8 X 5.5 prop was recommended, - you will be able to goto this size EASILY on that motor, however I think your 1320 mahr battery is the weak link in your powertrain.

Just my .02P worth

Here.

Cant comment on the wing loading issue, but increasing area will obviously inprove it - but add weight overall again! Why is it overweight?