I have the Goldberg one I built! The mods I made were beefing up the landing gear plate, glassing both wings top & bottom, glas cloth inside the engine box and I went to the aluminum landing gear and glass wheel pants and glass cowl.. The second time I flew mine, I landed in the tall grass and it fliped over. The plastic wheel pants that came with the kit cracked completly in half. That plastic stuff is real cheap junk.
I have a OS 1.08, slimline pitts muffler, with a 16x6 and it's a rocket. Flies like it's on rails. First flight was 0 trim on anything. Plane is very fast and be careful when landing. This thing does not glide. Come in with power. If you try to dead stick it in, make sure your're nose down and get as much air speed as you can. Once you're over the field it will land very nicely!
You may want to try low rates on everything but elivator as well!
Hi rates on ailerons is superfast. The first time I flew it, I couldn't count the rolls because it was soooo fast.

Have fun, it's a great plane.

If you are interested, I have another one new in the box I'll sell very reasonable.