Jim, I believe you will like a 26x10 prop better than a 27x8 with that big 40% Cub. Any of the engines that you mentioned will spin the 27x8 with authority. However, the Cub will look like it is in low gear with the engine reving high. IMO the Cub at 40% needs the extra speed available with a 26x10. Even with a 26x10 at full throttle, the Cub will not look faster than scale due to the size and drag. Of course, you probably won't be tooling around at full throttle all of the time. My favorite props in the 26x10 range are the Menz S and the Bambula.

Since you didn't mention twins, I didn't. I have a Brison 6.4 and like it very well. Both the 5.8 and 6.4 have mechanical spark advance and I have never had any problem with them. Some of the 3D fliers say that they like the mechanical advance better because the advance is more precise for hovering etc. I also have the CH/Syncro-spark on a Sachs 4.2 in my Bücker Jungmeister and it works fine. I'm sure that you can get the electronic advance with the Brison 5.8. It is simply a matter of locking the advance ring in place with a set screw and using a CH Ignition with Syncro-spark.

I guess you noticed on the Fox site that they didn't go to the trouble of showing you a photo of their individual gas engines. Maybe there is a reason that you don't hear much about Fox engines. Could it be marketing and over priced?

Keep us posted on your Cub project.

Ken