this is what i run on my e92:
http://hpashop.com/HPA-E82-E9X-Koni-...it-e82-e9x.htm
they make a version for XI as well for around the same price.
my advice is as follows:
1) Don't even consider springs without a strut upgrade. It's horrible. I don't care what anyone says.
2) Bilsteins are going to rattle your teeth out. They're unnecessarily harsh, especially for a street setup.
3) KWs are fine for comfort, but from my limited experience with them, they're too bouncy; likely due to the progressive springs.
My koni/swift setup is at the very least EQUAL to stock comfort (better IMO, but that is subjective) and is better than anything KW is offering from a pure performance point of view.
edit: and to be fair there are much better offerings that are in different classes, but expect to pay more than $2k for them.