Generally, it is considered that echo cancelling is needed on any circuit with one-way delay exceeding about 50 ms. A portion of the overall delay is caused by the transport delay in getting the signal from one place to the other. To give us a feel for transport delays, a delay of 50 ms works out to 15,000 km in free space, or about 9,000 km of fibre-optic cable. The delay on a satellite circuit is about 250 ms per hop. The algorithmic delay, or the delay introduced by accumulating enough data to compute a frame of data, is just one component of the total delay in the system, and comes in addition to the transport delay.
Additional time is required to compute the compressed signal and transmit it.
Note that you may achieve lower bit rates, but you also encounter more delay. You may be concerned about the amount of digital processing required for voice compression, as represented by MIPs in Table 1, but considering the progress being made in that area, none of these compression algorithms is likely to represent an excessive burden on hardware. Another parameter is quality of the sound. Minoli lists G.729 and G.723.1 as being of high quality. A Siemens document ascribes greater quality to the G.729 compression algorithms however.