Adding weight is like flying with the parking break on, one weak point of the magic is the fuseladge between the rear of the wing and the stab, if you put the pack and two servos in the tail and an heavy engine on the nose, it will be proned to breakage with a hard landing. you might try the following:

CF gear (use gear made for sig something extra from TnT)

Sullivan flex tank(1 or so oz lighter than a rigid tank)

feather throttle servo(save an oz or more and wont effect performance by moving aft)

dual elevator servos hs 85mg mounted under the horozontal stab(lighter and more torque than a std servo and will spread the weight out in the tail more)

this is probably stuff you have already heard but thought i would throw my 2cents in

Dan