Sounds like you have too much slop in your control linkages, and they are binding under higher air loads. Make sure your pushrods are well supported and you can get full servo travel while pushing on the surfaces to give a little resistance. If you are ready to venture into aerobatics, a 4*40 or Mid Star 40 are excellent choices. The Mid Star will overrotate at the completion of a long spin while the 4* does not, but I actually like flying the Mid Star more.