Sigrun,
"apples to apples" is exactly right. And you better have a very narrow defination of "apple". By that I mean, both planes have to have the same airfoil (including, and espeically the LE shape), the same wingspan, the same wing area, the same aspect ratio, the same taper ratio, etc.

So, if you have two 30% extra 330's, sure, go ahead, compare wingloadings. Got a 1/4 scale cub and a 1/5 scale cub? Forget wingloding, it's now useless as a way to compare those two. Heck, I'd even so far as to say that a CAP and an Extra with the same wingspan and same wingloading will fly "differently".

And that "anything below 30" is a totall laugh. I guess you've never flown a small plane? Too bad you arn't around here, I'll ballast up one of my .15 powered planes to 25oz/sq foot (well below your "anything under 30" rule), and I'll bet you $100 you can't fly it though some basic acrobatics, if you can fly it at all, I'll put $25 on a snap to the ground on launch all by itself). So, Chris, unless you qualify that with some more information, you're giving out some totally bogus information there.