I have over 3K miles on mine. They do get more compliant and softer however I travel mostly on highways so my experience may not be a good comparison. Yes, the suspension is stiffer going over rough roads (as with any car with a sport suspension). 300 miles is not enough to make a solid judgement. It takes at least 1K miles for the break-in period.
Maybe you should have stuck with the stock set up if it's too rough for you.
Take a look at the Bilstein review thread for more info.