I have an experience with H&R springs when I lowered my Toyota Altis 2007. Very nice pa din ang ride. One thing to look out for if you are going to do it is the progressive spring rate. Since the height spring is shorter, the spring becomes stiffer the more it compresses to provide resistance. Also make sure your wheels sill fit properly with your fender. Don't forget to get your wheels aligned afterwards.
About the 1.5in drop is what I can recommend. Had no problems with usualy humps axcept really large ones in exclusive villages and provincial railroad tracks that are elevated.
Hopefully you'll enjoy it.
As with all the things in the world, expect to pay more for higher performance and dependability.