Though there are 30k searches, you of course wont get them all, and even less as you move down the ranks. As said, better to go after many keywords, rather than just one phrase.
Not to mention, why go after a phrase with free in it? What type of traffic will it be? Most likely freeloaders just looking for more free porn they dont have to pay for. Not to say you could use the traffic is other ways, I'd rather go for the people that might buy something..
ronnie