There is no hard limit on MeasuredBandwidth. Given an infinitely fast network, the maximum bandwidth sustainable is determined by the performance of the CPU and memory, and will vary depending on the Roku model. As for why a rebuffer occurred in the scenario you mention, it's hard to say without more information. A nominal "2600 mbps" stream normally varies somewhat over its duration; at one point it may need a higher bandwidth and other spots it may need less. The nominal bandwidth is an average, and depending on the encoding, there may be spots which require much higher bandwidth. Also, very sudden changes in network bandwidth may not be reflected in the MeasuredBandwidth value. In the extreme case, if network activity completely stops, the MeasuredBandwidth value will start to decay and eventually reach zero after a couple of minutes. Measuring network bandwidth is by no means trivial (or even well-defined in all cases) and there is a tradeoff between overreacting too quickly to short-duration changes in the network, vs. not reacting quickly enough to longer term changes.
--Mark
