I'm not a guru but have owned several small refractors, all achromats, and have observed with many small and medium ed's. That said, I would venture to say that on most nights with average seeing, you would be hard pressed to really see much improvement from an ED or APO design over a good long focus achromat in the 80 to 102 range. When you get to the 120/127 and larger category the color defects of the achro will start to show enough that you can readily see the difference. Color aberration will be the first noticeable failing. The next will be softness at higher magnifications when the atmosphere allows those attempts. I can remember one night years ago when I was observing Saturn at approximately 300 x in my 127 f9 achromat. The image was actually very good, even confirmed by many others. Until a fellow club member put the club's Tech 140 on Saturn. Below 200 x there really wasn't much difference to be seen. As soon as the power went to over 350 the difference was very apparent. You really have to ask yourself how much time do you plan to observe at the high powers. If not much then be very happy with the nice scope you already have!
Walt
Walt
