What engine are you running? These planes are really intended for .40's and bushing .46's like the .46-LA and they perform very well with that kind of power. That doesn't stop people (like me) from bolting a .46-AX or even more in the nose.

I've seen catastrophic wing failures on these planes from excessive speed, often in a dive. If you have a big engine and you're looking for maximum speed, it might be worthwhile to add some fiberglass to the wing center section and maybe even beef up other parts of the wing structure.

As Hogflyer pointed out, look at the aileron torque rods. Any slop there could lead to problems. If max speed is your goal, you might want to try upgrading to dual aileron servos with a tight, short linkage. Even then, the problem might not be cured if you go too fast. Counterbalancing as suggested by JohnBuckner might be another option.

Going insanely fast is a lot of fun, just understand that there are trade-off's and something could fail.