cwojcik
70cc twin V2
Depends on the 60cc airframe.
11.5 lbs on 1000 - 1100 squares for a 3DHS gasser
15-17 lbs on 1426 squares on the Aerobeez
21 lbs on 1650 squares on my buddies EF 91 extra with DA-60/RE2.
30lbs on 1900 squares on my EF 104 extra.
I know my big plane floatier than my 30cc stuff. The wing loading is much higher though. Reynolds number come into play. I need to dig out my aerodynamics text books from college.
This is why cubic loading was invented: http://www.ef-uk.net/data/wcl.htm
This question has different answers depending on what your mission is. If you want to fly hard and practice 3D/XA/precision, go for a good 30cc plane. Invest them time in making it work well. The EF 78 Extra outperforms many 50cc airplanes from cheaper manufacturers. However, the engine choices for 30cc aren't quite as mature as 50/60cc, and the larger sizes can be easier to see and land. So if you are a sport flyer that just wants one of them fancy lookin' 3D errbatic planes, you will likely be satisfied with a cheaper 50cc set-up where you don't mind wing rock and coupling because you won't be doing any low hard 3D or IMAC, and you won't be flying hard enough to blow back servos or notice bad centering. If you have aspirations of being a 3D star then you will be better served by getting a good plane with no vices and spending time and money on a good engine and perfect servos.