Just finished testing all the OBD II dongles I have available currently. Using the ECUsim2000 (which simulated a car on my desk), the results can be compared directly. For real cars, rates will differ depending on the bus protocol (CAN or older, the ECUsim has been configured to use CAN 29 bit/500kbps). The values shown can be considered to match late car models. Speed-wise, Bluetooth devices are slower than wifi dongles - they require less energy and are easier to handle on the other side. The fastest wifi dongle I tested is pretty old, it is a first generation Kiwi Wifi. I assume current wifi dongles can achieve even better values. I will constantly complete this list. In case you have a dongle available I'm missing here, please visit us in Cologne and we will test it.
[21st Mar 2014: initial list]
[30th May 2014: added OBDLink MX Wifi]
[2rd July 2014: added GoPoint BT1A and Porsche 911 GTS]
[15th July 2014: added OBDLink MX BT and OBDLink LX BT]
[18th March 2015: added variants with multi CAN requests plus RaceCapture/Pro MK2]
 
- Harry