[bodywerks]

I have experience flying at 7,000 feet with a 50cc gasser, so I can tell you that you NEED not just a light wing loading, but also a light plane. For a 50cc plane, you can hover 16 pounds (this is at 7,000 feet with about 10,000 feet density altitude), but you won't be able to pull out with any kind of authority, if at all.
With any 50cc plane, equipment choice will be highly important. This means no power expander, choke servo, battshare devices, etc - just batteries, servos, and receiver. For batteries, I am talking like a single 2100 lipo and lightweight regulator, or a single 2300 A123 (better yet would be a single 1100 at only 3 ounces!), and a little 1320 lipo or A123 1100 for the ignition.
Of course, for this to work, you need a 50cc plane that balances easy without needing all your batteries hanging off the front of the engine box to balance. Otherwise, all the efforts to safe weight are a waste.
The EF Yak is awesome, but I think it comes in at around 17 pounds and needs all battery weigt forward. If I were to go that route I would definitely at least get a EScomposites carbon fiber tuned pipe to add some extra power without adding a ton of extra weight.
I think Wildhare makes a few 50cc planes that finish out under 16 pounds pretty easily, and 3Dhobbyshop has a pretty sweet-looking(and reports say it flies better than it looks) 300SHP that has tons of wing area, is light, and balances easily with a 50.
Another option is to go with the EF Yak that you like and put a little more motor on it. I think Brilleli makes an engine in the 60cc range that is pretty light, for example.