ARBs....
Some people recommend removing front arb altogether and leaving the rear on to give a more neutral too rear bias. But I'd only do this for track use or if you are used to a rear bias. You could get dramatic lift off oversteer!
Good for fast road use is the matched Eibach set apparantly, not adjustable but suited to road use.
Thicker than Eibach is Neuspeed, and these are adjustable.
Thicker again is H&R, also adjustable. although more suited to track use.
Go too stiff and you will get alot of uncomfortable side to side movement over broken roads.
Adjustable bars a better idea for track use, as you need access to a track to set them up correctly really, so not so good just for road use.