As said before go ahead and take it out. I dont know how Lou says that it wont effect the performance at all? He has been doing this for a while but all of the planes in which I have taken the diheadral out of performed much better. I say if it takes the self righting effect out of the airplane then it is reducing washout and thus will respond better to your input. It seems to me that if the airplane is fighting you to come back to center b/c of the design of the wing then redesigning the wing would allow the control surfaces to have more effect as far as the roll rate goes. Plus a flatter wing is better for inverted flight (this has to do with the airfoil as well). You might also want to try to shorten the wing??? I dont know how comfy you feel with going this far but it will make the airplane fly all together different. If you notice hightly aerobatic high wings (citabria, decathalon) you will notice that the diheadral is little to none (depending on how many modifications have been made ). If the amount of diheadral doesnt effect performance then why wouldnt the manufactuers leave it in order to provide more stability on landing?? Maybe I am totally off base here but from my experience of redesigning stuff it always seemed to help performance.