RE: GP Patriot 40
this is my old patriot. (i sold it a short while back) same setup as you describe. i finally settled on a 10 x 7 prop with the 55. the c.g. was dead on 8 1/2 inches. i only used 1 4.8 rx battery. my reciever was located as far back as possible. the retracts may have made the difference. also as stated above i used foam tires. as summerwind says dont slow on landing, keep speed and fly it all the way to the ground, there will be no suprises if you keep your speed up .also be sure to have plenty speed before rotating for takeoff. good luck on maiden.
as i was posting pics figured i would add a couple of my other propjet. has OS 61sf. this one is a bit more of a handfull than the patriot.
if you want to see something really insane, do a search on youtube for the twin patriot with rocket assist. you talk about fast !!