It's quite simple - for 2 cars of the same type and weight, more bhp = more acceleration. Torque is misleading because it is multiplied by the gearbox and final drive, and high revving petrol engines will multiply torque by about twice as much as a low revving diesel. To eliminate the gearbox effect, you can multiply the torque by the revs. This new comparison amount is called, er, power.
At mid revs the diesel has more bhp than the R. So at mid revs the diesel accelerates harder than the R does at mid revs. But at high revs the R has more power, and so accelerates harder. The net result is that a standard R is a bit faster than a chipped diesel (as you'd expect).
