I know if I was sitting at the back as a passenger on a take-off from as limiting a contaminated runway as you like, if the choice is available to the pilot, I would like him to stop and take my chances with an over-run than struggle into the air on one with an active fire warning going. Period. You can produce all the scenarios you like about how difficult it is, but it has been factored into the calcs and if stopping at V1 is open to you and you're burning, you're a darn fool not to! The firewire is pretty foolproof and failsafe- if it is blowing the warning, you must assume there is a genuine problem.
Realistically, on a twin, your acceleration is bewildering. Speed is building up so fast that at a few knots below V1, you don't have thinking time. You must go into automatic and not take a shoot-from-the-hip decision trying to factor in runway state/length/wind/slope. It's just that sort of decision making process that gets you into big trouble! Then you must imagine sitting in a witness box at a Coroners Court explaining your decision to go against rules and regulations.