I've been flying the GP Space Walker with .91 Surpass power here at 6300 ft. elevation for about 4 years. No problem with stock firewall. The plane needed that much nose weight anyway, and I would not say it's overpowered.
It's a great combination and a real pleasure to fly. My plan is to get another to keep "just in case" because I think I'll always want to have one. Anybody comfortable flying a 4-channel trainer should make the transition to handling the Space Walker quickly and easily. A couple of flights on the cord with instruction might be a good idea. Because of its size, things don't happen real quickly, so you want to be well ahead of the airplane even though it flies pretty slowly.

As to the 4-Star, it's proven itself for years as a good intermediate's secondary trainer and general sport flyer. I don't think you'll go wrong with either.