RS:

Tip plates do limit tip vortices, but they also increase the tendency to snap. Further, with the ends of the ailerons so far in I don't think the tip vortices are having any effect. Same comment for tip sweep, or Hoerner tips.

You say you have all the slop out of the linkage. Including the gear lash in the servos? You might replace all the pivots with ball joints, another thing that sometimes helps is increasing the mass of the links - either use heavier material, or wrap a layer of solder, stick it with CA, and cover it with shrink tube. If there is any slop at all in the horn pivot this wont do any good. Ball joint pivots are best.

My first choice would still be the weights in the leading edges of the airerons. But the solder wrap is the easiest/fastest.

Aileron separated?
. Plane's not man-rated.

Bill.