Hard to say with the ever changing price of LLLL. wfox is not copywrited, but I can see fox being crazy like other companies and try to highjack it from you saying its a typo of fox.com (hopefully that wont happen, or you have lawyers).
600 seems to be a fair price at the current market though. You have to guess though whether the market is going up or down. Alot of people are saying that it's a bad time to sell, but some people are also speculating LLLL value to decrease. I am personally one of those. I think LLLL was overhyped and only had temporary value because all the domainers bought them out.
You can find 5-10 LLLL.com drops a day if looking right... Not sure end users have a demand for them.
Personally if it was me, I'd sell for 600$ maybe try to get slightly more but I think its a fair price.
Good luck!