The Ford RS200 E1 might hold the Guiness World Record but in FIA Group B rally terms it was never the fastest of the breed and it never won a World Championship Rally against the dominant competition in the 80's which were the Peugeot 205T16 E2 and the Lancia Delta S4.
Both have spaceframe chassis, over 600 Bhp and 4WD with viscous coupling variable 40/60 front to rear split. They ARE officially FIA homoligated production cars as much as a Skyline GTR is a Group A car as the manufacturers have to prove they built 200 identical cars before they were granted homoligation for Group B. They were road registered and the general public could buy road going versions with leather trim etc.
To allow an Evolution model into a World Rally they had to build 25 versions all using the newer parts. It may not be the 25,000 min base models they are required to start with these days, but current day rally cars are not built in any thing like batches of 200 vehilces.
It is reported that the Lancia Delta S4 car do 0-60 mph in 2.9 seconds ON GRAVEL. As a spaceframe car with kevlar panels, 650 Bhp mid mounted, supercharging and a huge turbo plus a viscous 4WD (which works in the reverse of a standard open differential and directs power to the wheels WITH the most traction) anything with 2wd and/or steel panels starts with a serious handicap.
If only either of these two cars were tested for the World Record on tarmac who knows where the record would stand.
My bet for World Fastest 0-60 in any classification is the new Mitsuibishi Evo9 EV with 4 in wheel electric motors, 200Kw and over 2000Nm of torque from 0 rpm. That would make even a Delta S4 look agricultural.