WHATS THE RIDE LIKE COMPARED TO STOCK RIDE?

The Eibach Pro-kit does not have a very stiff spring rating. Eibach has always generally been pretty comfortable as far as ride quality, even on the 79-04 Mustangs.

If you just swap the springs out, without changing shocks, you may have a rougher ride than stock, nothing that will break your teeth though... with shocks, the ride will obviously be smoother and better dampened.