but will not burden the model with the extra nose weight of say an OS.91 or Magnum .91. Not that the latter two engines do not do a good job of powering the model. Their extra weight can be problematic in some instances.
Ed: I also agree with most of what you said, but I do need to correct you on the above statement.
The OS 61 2-stroke weighs 23.4oz with muffler. The OS 91 4-stroke weighs 24.2oz with muffler and the Magnum 91 4-stroke is about the same. I doubt that 8/10 of an ounce is going to be problematic in a 7-8 pound airplane.
Jim