Do I understand you correctly that your tail 'kicks out' in tight cornering? If so, a heavier rear bar will not solve the problem at all. In fact, tightening up the back will tend to make the car oversteer even more. The best thing you can do to reduce oversteer is to induce understeer - by stiffening up the front. If it were me, I'd do both, just to be safe. Most likely the suspension has been worked on by the aftermarket manufacturer to perform the best (safest) under these conditions.

On that note, I noticed the other day that Road and Track (?) had the V40 listed as having the worst cornering (lowest g factor) of any car they've tested in several years. I haven't had the opportunity to throw my wife's V40 around much, but have noticed that it's significantly slower than my car (Subaru SVX) around most curves in the area. All of which makes me think that the best possible thing I could do improve the handling would be to drop the CG - i.e. lower the springs.

Any thoughts? Agree/disagree?
--
Steve