I would not recommend stiffer front anti-rollbars to improve handling. It will probably get worse instead.
For the Viggen SAAB used a softer front anti-rollbar to reduce oversteer. Hirsch Performance does the same on their tuned SAAB's. The idea behind this is that a very stiff rear anti-rollbar can cause oversteer when cornering at very high speeds.
This thread on Saabscene
might be interesting if you want to know more about front/rear anti-rollbars.