Yeah, the len10 challenge did not live up to all the hype.
They didn't have enough wind for megaloops, so instead they did a regular to big kiteloop comp. Mega airs start at 30ft (Hadlow
http://www.youtube.com/watch?v=M7dc7DG-qb8 ), most would say more. And although it's extremely difficult to land, you want to get in line (or pretty close to that ) with you kite.
So megaloop = Getting in line with your c-kite at least 30ft up and in base winds no lower than 30knots. Anything else is a big kiteloop.
You need to be at least 30ft since you will drop, like you were hanging onto a huge rope swing, about half the length of your lines (20m lines). So once your technique is down, go as big as possible for safer landings.
Here's a more recent megaloop comp called N.A.P. put on in 40 knot gusts.
http://vimeo.com/45130023#
Len10 shows he's still the best with 40ft backroll tailgrab megaloop adding a second backroll tailgrab as he steers a big helicopter loop to land. There was also a nice kiteloop, barspin to double fist pump at 2:42. And the last kiteloop at 4:45 is probably one of the most critical I've ever seen landed. By critical I mean the kite looped below the rider and he needed every foot of the original boost to land it.
One thing is for sure, those Dutch have a special gift for megalooping.