I have had several bipes and I like the ultimate the best. The Sig hog bipe is a nice 60 size plane and will fly nicely on a 91 4 stroke. My GP 40 size ultimate was my favorite flying plane until I got the bigger Goldberg ultimate. The GP flies great but is a bit hard to see in the air as it is small. It is also the easiest one to put together at the field. The Goldberg is a 60 size plane but needs a bit more engine than is recommended. You will either need a 90 or larger 2 stroke or a 120 size 4 stroke to fly this plane well. Mine has an OS 120 4 stroke and it has unlimited vertical. I also have a 1/4 scale ultimate with a Moki 1.80 on it. I just installed the engine in it and have not flown it yet with this engine. It had a ST 3000 on it and flew very nice. I was converting it to gas but ran out of $$ so it gets the Moki for now. The red one is a 62 inch Chuck Cunningham Lazy Ace they are hard to find but fly nice. Here are some Pictures.

Rick