RE: World Models Extra and Slick 540
What do you want out of the plane? If you want a sport flyer, then it will fly fine. I've flown two TWM warbirds and they fine models and fly good.
If you want AT ALL to do 3D, don't even consider them. Spend a little more and get a 3DHS 59" Slick or an Extreme Flight 60" Edge or Extra.