RE: Falcon/Bobcat 25 motor?
on 6s a 3600 Kv motor would try to turn 75,000 RPM. A prop of 0" diameter and "pitch would come close and pull few amps but go now where. As you increase in diameter and pitch the load increases and the revs decrease as the amps go up. By the time you got to a 4x4 the amps would probably be in the 100 amp+ range giving very little thrust and wasting a lot of power as heat unless it was a very heavy motor and supplying 100 amps would require heavy batteries.
Unless your chasing a speed record you may want to reconsider that approach since it would make for a plane with a very high wing loading and very low thrust. It would be hard to get off the ground and stall violently if you went below stall soeed which would be high. The vertical performance would also be very poor, in fact the only positive would be high pitch speed.
Inrunners have some destict disadvantages for direct prop drive applications, they are too high KV for a given weight and have worse cooling by design limiting power to weight ratio. They are great in ducted fans since they require very high RPM and force cooling air over the motor. If you want to use a fan on this I'd go with a 70mm up to perhaps a 90mm but it will take a lot more research to find the right combo for that airframe unless you find someone that has found one and copy it exactly. Search RCGroups in the pusher jet forum and you should find some conversion threads for 70mm IIRC.
If you want to go the direct drive route you may want to download Scorpioncalc and play around with it. even if you don't buy a Scorpion you can find a motor wtih similar characteristics and get in hte ballpark.
I have one sitting in my "to build" stack near the bottom with plans for a fan and retracts some day.