RE: CG Ultimate or GP Super Skybolt?
No debate here. You want to build the Goldberg Ultimate! It's easy to build, looks great, and flies amazing. You want to have 2 aileron servos, fiberglass cowl, pants, and aluminum gear from Stan's Fibertech. I've never built the GP Skybolt but I have seen it in the bones and flown one. It's got a balsa wood fuse that looks like a real PITA to build. It also appears heavy and slightly smallish compared to the Ultimate. But, more importantly, I don't think it looks as good (my opinion) and it certainly doesn't fly as well as an Ultimate (fact!) The skybolt has a small tail and an unswept bottom wing...it's really not an "unlimited" aerobatic machine. It has funky yaw-pitch coupling that makes knife-edge flight, etc. a pain. Likewise, the ailerons are a little small for my tastes.
As far as your other issues...I've owned at least 100 airplanes over the last 15 years and I've never once had to take out a properly installed fuel tank mid life so this is really a non-issue.
I've had both the wire gear and the aluminum gear on the Ultimate...if it's light, the wire gear is strong and bend-resistant other it has a slight fore and aft shimmy. The aluminum gear (1/8 inch) is a little weak but certainly looks nicer. Maybe someone out there makes a slightly thicker gear.
Prop clearance is a non-issue on the Ultimate. A YS 1.20 or 1.40 is the way to go...totally unlimited performance.
Have fun with this plane...it's great.
Mike