I dont feel qualified to comment with some of the heavy hitters in this thread due to lack of experience, but from what ive read on the board plenty have run 20 lbs + with only a slic on 93 no alky, username ikle comes to mind..
I would "guess" that a front mount would enable you to run 19lbs w/out alky but that might end up causing other issues ie surge, lag, mismatched combo etc... literally my 2 cents