However, does any one have any data on rates of decel using reverse thrust alone?
Intruder has supplied the info you need. See page 5 of the NASA document which shows the Force given by the Reverse fans for a DC10-10.
The Reverse thrust force reduced from around 30,000 lbs at 140 kts to around 10,000 lbs at 20 kts. If you assume an average of 20,000 lbs force on an aircraft weighing up to 421,000 lbs landing weight, then the deceleration due to reverse thrust alone is about 1/21 g i.e. about 1.5 ft/sec/sec or (0.5m/sec/sec).