well a few things,

in the GTI and Golf it is 1 10" in my m3 it is 2 8"

i think the 10 probably hits a little louder.

That said, if you are not a "bass head" yah, they are great.

if you are used to a 10"s or 2 12"s and 300-500 watts, then no.

I am pushing about 200 watts to the 2 8"s right now and i will say this.. i can't believe how much frequenzy response they got out of them. they have a great range.. so far i am very happy. My only prob is that since i bridged teh rear channel of my ppi i can't gain up too much.. when i do they HIT HARD, really hard, and LOW, i am stunned they can get that low, it is 2 8"s in an infinite baffle setup. So to answer your question, they are great for sq, and sound great... but i doubt they = a custom box with 2 10"s then again, i didn't want neighbour waking sonic death boom rattle your heart out of your chest bass, although i CAN achieve it with the stealthboxes, i would have to run more power.

Check out vwvortex.com a lot of guys over there have them

Let me finish by saying, if the 8"s have this kind of response in an infinite baffle setup, i would imagine the 1 10" in the spare well would sound PHENOMENAL.