Here is my 1.8 20VT lowered about 80mm on my current 18's...
Here is my old 1.6 16v lowered a LOT (100mm approx) on my lurvly 19's...
Ride quality is obviously not as good, but scarily nimble round the twisty stuff. Depends what you use it for. I went for 18's for a few reasons, cost being one of them. You can go for big rims, and loooow without scrubbage, dont let anyone tell you you cant. And yes the ride quality is not as good, but you get acustomed to it.
Basically, the PRO's far outweigh the CON's.... bo BIG, go LOW