I have the FRPP springs... same decision as yourself... I live on a hill, that is on a hill... so have to clear a little ground upon leaving the driveway (take the driveway out on an angle). So I cannot go too low here.
I will say this, I love the FRPP springs. their look for sure! and they ride SO much better than the stock springs - both comfort and performance. Their drop here was a little more than stated... so I eventually dropped almost level in height (the rear dropped more than the front - so looks correct!!). But I would say their drop was almost an inch maybe all around. Makes the SnowFlakes look soo much better, as far as fit. (still thinking some 18x9 rfp-1's in gold or bronze to really finish it off).
I started with Steeda rear end links... then the FRPP springs and brakes all around (just R1 concepts - no big brake kits yet...). Stock struts/shocks. 15k on the FRPP and no strut issues! added the Steeda rear sway bar (waiting on weather to break for the front swaybar and wheel alignement). I have designs on the Bilstein B8 all around also!
Not saying anything bad about the Mountune, as folks that have them love them too.
A friend near by has the mountune kit, Bilstein and springs, and his drop looks the same as mine. His ride feels very similar to mine own. So if you find a deal on one or the other, like Ebay for the FRPP springs, or ModBargains for the Mountune... go for it! In fact Modbargains has a good price on both the Bilstein kit, and the mountune springs... Just sayin If you can find a discount code for them, or call and ask, for 850 less a discount, hard to beat...