I have several questions for you. I'm not picking on you but trying to be realistic so please do not read anything into it.

Can you grease pretty much every landing?

Can you fly your trainer inverted for at least 3 patterns around your field and be completely comfortable doing it? (RCKens's favorite thing and it works)

Can you put your trainer EXACTLY where you want it?

If you answer yes to all of the above then go with the UCD. If you answer no to any of the above stay away from the UCD. Yes they fly nice a slow, and as I have said time and again, easy to fly is a relative term. Since you mention that the people at your field say to get one, that's a pretty good indication that someone has one. If so ask to buddy box with them.

UCD's cannot be manhandled both in the air and on the ground. One good hard bounce and you will be walking out to pick up the landing gear and plane. They are a true 3D plane and as such are built very light and cannot take allot of new pilot punishment.

I am not trying to discourage you, I am simply stating the fact as the plane stands out of the box. You can reinforce the plane to make it stronger but weight is the enemy for 3D.

Now as far as the 61FX versus the 91FX, the 91 will fly the snot out of that plane. Pin the firewall if you go with the 91 2 stroke. A 91 4-stroke will fly it well but it will not be a 3D monster although it will fly 3D decently.

Chad, since you appear to have great knowledge of both the 61fx and 91fx what prop would you recommend for 3D flight that will give great vertical on the 91?