Even if you had a shock-horror moment on hearing the bell (as most of us would) and actually reached V1 before rejecting, in my opinion that would be the safer option because as old Smokey says, in the air a fire could destroy the vitals in 3 or 4 minutes. Better to go off the end at 20 knots, grind to a halt, get the pax out with a few broken limbs than to be faced with a Concorde-type situation in the air. And really, how often are you really, really stopping distance limited in a B737 from V1? On 25% of all take-offs? Depends on where you operate I suppose. So then we get into the actual odds of running off the end if the reject is actually commenced bang on V1.
At V1 minus 5 or even 10 knots you do not have the luxury of assessing how serious the fire is. You have to assume the worst and do what most briefings state in one form or another - reject for any situation which could make the airplane unsafe in the air. Argue the legalities of what constitutes V1 from the safety of the courtroom, not from the grave.