1.4 inch drop ...thats your best bet..you wont need to replace shocks and the ride quality is really nice...i didnt notice ANY difference in ride when i lowered my car..i actually noticed a much larger difference when i got my rims. 2.5" is RIDICULOUS.
2,5" isn't ridiculous. Not if you've got BIG wheels. I've got a 2,7" drop rear and 2.3" front. Looks just right, sitting on 19's.
And, as it already has been said: the lower you go, the more you'll feel every single bump in the road. And what tyres you're running also has a lot to say. The lower the profile, the more you'll feel everything.