I have a 40size cap also..

At first I had a GMS .47 in it, and like you said gutless.. it flew ok but needed more power.. Then I installed a SuperTigre G.61 then it had good power but now she was heavier.. It's a viscious circle you fall in.. My cap is so nose heavy that it comes in like a ROCKET and I can't move anything back any further... If you are looking for 3d flying then go with the FS 90.. My .61 just had enough power to keep it hangin on the prop for a few seconds then she'd fall over..

I would suggest a 120 size cap.. better flying characteristics than a 40size....