Jetta with 17"wheels, thinking of lowering it..

I have 17" with 205/40/17 Nankangs Ultra Sport NS2 all round, I'm thinking of getting the FK Sport Edition Plus Mk3 Golf / Jetta Coilover Suspension Kit-Adjustable Shocks from ECS website or the EIBACH PRO SYSTEM KIT 8552.780 from www.dotcomparts.com... anyways with that said, how low can I go without rubbing? The eibach system gives me a 1.4" drop and is cheaper, the FK coilovers give me a 2.1" to a 3.1" drop. There is only a 150$ price difference between the two, are the coilovers better? Will it rub with the coilovers at a 2.1"drop??