Instead of answering the question asked people jump straight to 'its fine'. While true, this doesn't answer the question that was asked.
Is it overkill to run 50 feet of LMR-400 at 6 meters frequencies? Yes. But then LMR-400 is overkill most of the time it is used...
Any quality half inch diameter coax will work fine for your needs, and honestly, if it were a portable setup or one that required some fairly sharp coax turns between the radio and antenna I wouldn't hesitate to run even smaller coax than that. You won't notice any difference between LMR-400 and, say, Belden 8215 (RG-213).
thanks for the input DB. It's a base install. Once up, I hope it stays up for awhile. Coax will go from antenna to multi switch. 73
The DB