Hi Styria this is American 6.9 performance from Car and Driver . Zero to 60 mph: 7.1 sec
Zero to 100 mph: 20.6 sec
Standing ¼-mile: 15.7 sec @ 90.9 mph
Top speed (observed): 133mph
Braking, 70-0 mph: 207 ft
FUEL ECONOMY:
EPA city/highway driving: 10/14 mpg
Now here is Euro
Complete performance analysis and accelerations review for Mercedes-Benz 450 SEL 6.9 in 1978, the model with 4-door sedan body and V-8 6834 cm3 / 416.5 cui, 210 kW / 286 PS / 282 hp (DIN) engine for Europe . According to ProfessCars™ estimation this Mercedes-Benz is capable of accelerating from 0-60 mph in 6.9 sec, from 0-100 km/h in 7.2 sec and 1/4 mile in 15.4 sec.. Below we present more detailed data of the official factory claim and the ProfessCars™ estimation, including acceleration times 0-100 mph, 0-160 km/h, 0-200 km/h, with comprehensive graphic illustration, top speed, accelerations on gears and
http://www.automobile-catalog.com/performance/1978/1470470/mercedes-benz_450_sel_6_9.html
Apparently the AMG 6.3 had 320hp and did quarter mile in 14.5 seconds
http://www.automobile-catalog.com/performance/1971/1567745/amg_300_sel_6_3.html . which is also what magazine did with standard 6.3 .

. 6.9 had a factory rated top speed 10mph faster than 6.3 but is was slower by around 1 second over the quarter mile Styria . One is a Bankers Hot Rod the other an Autobahn Bruiser.
