4 - 5 inches and you will be basically on the ground and not really driver friendly.
Other than that I have not been able to find actual parts specific for kymco that are made to lower the scooter. but I have toyed with the idea of getting ruckus lowering forks and trying to fit them. HOwever, I don't feel the need to spend the funds over $100 US to get them and them not work. I have other ideas but the electricals won't hold for a compressor to air ride the scooter.