I don't know of any 4 stroke that will haul a 25 lb. plane.
are you familiar with the Saito FG36?. a big four stroke gasser. will haul that bad boy around with ease and sound good, as well as giving you a nice slow idle and fly on tiny amounts of fuel.
thread is here.
http://www.rcuniverse.com/forum/m_5041020/tm.htm