The bottom line is this; all aircraft, 2, 3, or 4 engines, must meet minimum climb gradients with One Engine Inoperative (OEI). As previous posters have stated, these are 2.4%, 2.7%, and 3.0% respectively. There's not a huge difference between these.
On the day that an engine doesn't fail (99.9999% of the time), the 2 engined aircraft has an EXCESS thrust of 100% above minimum requirements, the 3 engined aircraft has an EXCESS thrust of 50% above minimum requirements, and the 4 engined aircraft has an EXCESS thrust of a mere 33% above minimum requirements
So, if I have an engine failure, I much preferred the times when I flew 4 and 3 engined aircraft. On the 99.9999% of occasions that I don't have an engine failure, I
MUCH prefer to be flying an aircraft with a 100% thrust reserve, the twin!
Things like wind shear, Middle East low altitude inversions etc. come to mind...............
Regards,
Old Smokey