It wasn't that the 5 was faster, the problem was the inertial alignment reference system was allowed to operate for 40 seconds after liftoff.
The same system was used in the 4 and 5. The failure was caused by the quicker rotation onto the orbital insertion trajectory used by the 5. At 37 seconds after liftoff, the horizontal velocity value generated by the inertial reference overflowed and caused it to spit gibberish into the inputs of the guidance computers. Since the IR wasn't being used, the engineers assumed they could safely ignore it, and leave out any error trapping on the IR's data output.
The backup computer crashed first, then the primary. When the failover system attempted to switch to the backup, it was already gone.
With garbage data running rampant through the system, the engine nozzle actuators tried to do a u-turn.
Had the primary guidance crashed first, there might have been a slim chance the rocket could've kept control through 40 seconds, when the inertial reference would've shut down and stopped sending garbage data.
The rationale for leaving the inertial reference running past liftoff was so the controllers could disable its shutdown in the event of a late pause in the launch sequence. If allowed to shut down, the reference would take some time to re-align.
A better way to have designed the system would be to have the inertial reference shutdown event triggered (by actual liftoff) rather than time triggered x time from countdown start.
IIRC, that was the fix for later launches.
Even better would've been to leave the inertial reference out completely, since it wasn't actually being used in the 5! A dummy box that did nothing but output a constant "safe" value, ignored by the rest of the system, would've been cheaper and also solved the issue of "designing out" the IR interface.
Quite annoying to have an expensive rocket and payload destroyed merely because someone assumed an unused bit of equipment could be ignored completely, without making absolutely certain that it would not have any effect.
If the Ariane 5 was a car, it'd have an extra gear in the transmission, which at certain speeds and angles of turning the front wheels, would engage and make the car do a u-turn.
August 3rd, 4th and 5th, 2012
"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus
, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".