since all LLLL.com's are gone, I would expect them to appreciate even more in the next year or so, if you can hold onto to it for another year, I would easily say mid $XXX for your domain!.
Yes it is a triple premium, but it also has some other interesting things going for it. There are a lot of company intials, and acronyms using 'lmk'. 'n' is an intial used for networks, networking, nation, etc, etc.
But more interesting to me is keyboard geography. People remember things aurally, visually, gustatorily, smellatorally and also kinesthetically. People can't smell or taste a domain ... yet, but people do remember domains by seeing it on the screen, seeing it typed on the keyboard, and feeling the pattern their fingers make by typing it.
On my QWERTY keyboard, LMKN are next to each other and typing the letters makes a distinct pattern. I believe this aids in recall and makes this superior to random triple premium letter domains.