You can lower the front quite a bit with the stock bars, but the problem is that as you lower it you have to readjust the camber/caster/ and toe. If you go too low, you'll run out of the stock suspension's adjustability and won't be able to correct it completely. A half inch should be no problem. If you want to really lower it, you might want to invest in some tubular UCA's, most of which have a better out of the box setting for modern tires and are adjustable to boot, to keep the alignment specs in order.
