Foster would stop Hagler. I happen to think that was possible for Hearns to have stopped Hagler at middleweight had he not broken his right hand in the first round of 'The War'. So if I believe that Tommy can do it at MW than Foster definitely can at LHW.
He fought a few cans at around 168, coming in at 161, 162 ect, but this thread was to settle a debate. Which I won handedly.