Iam looking at lowering springs for my t4 1.9td and iam puzzled about which ones to buy? Eibach, h&r, vogtland. I want best under fairly heavy load as iam a carpenter and van carries tools and some materials.Van wheels are 18". Wish to lower by 40-50 mm.some springs are progressive? Iam new to this and would be grateful of any advice of people in the know!