Interesting. I agree 2 strokes are cheaper and DO spool up faster (they can rev from 5K to 17 K in the same time a 4 stroke revs from 4K to 10K) however, you'll never see the plane actually MOVE faster than the 4 stroke powered one -- just the opposite. You get more "whine" and less "pull" with a 2 stroke. The props are smaller, and the torque over the useable (hovering) mid RPM range is less with a 2 stroke.

Concerning durability: After crashing a 4.5 lb tufflight 4D well over 100 times (many, many of these resulting in buried engines) with an OS .46 FX, I can attest that this motor is a good durable one. Two other friends I fly with had similar experiences. The only issue I ever had with the OS was the carb screws had a tendency to fall out, but that was solved by some loc-tite. HOWEVER, after I put a Saito .72 on the same plane, I was pleased to find that it too could survive crashes. And the best part was that the carb is in the rear, so it wouldn't fill up with dirt. I could just replace a prop, clean the dirt out of the fins with a toothbrush, start her up and go practice some more.

A Saito .72 saved my butt MANY more times than the OS .46 ever could. I can't count the times I was doing something crazy low over the deck and punched the throttle when the plane was getting hairy, and thinking "Wow, the 2 stroke could never do that!"

2 years ago I filled out the R/C report questionaire category "best R/C related purchase within the last year" as "my Saito .72". I still think it was worth every penny. They get stronger with age too! Can't say that about an ABC engine!

So, if you plan to fly a LOT, and you consider the cost of your time, it doesn't make sense to skimp on the motor. In my book, unless you actually prefer the whine of a 2S to the "Harley-esque" thumps of a 4S, there's no reason to use a 2S for 3D. If it's an issue of cost, save that extra 100 bucks you were thinking about for the next plane. Drink less beer. (did I actually type that?) Well, you get the idea. That extra 100 bucks goes towards power and reliability you can almost bet your life on.

Rich, if you do want a used motor, now that the .82 is out, you should be able to get used .72. The power isn't really all that much different ( I find that a friend flying his .82 on 15% nitro is roughly equivalent to my .72 using 30% -- both motors on the same prop, same weight airplane).