I will start to explain the choke phenomenon since it has a vital affect on game play and net code settings.

Choke
Choke is determined as follows:

The next time a packet can be sent is:

Current time + 1/cl_updaterate

Current time + (number of bytes just sent / rate setting)

So, if you play with a high cl_updaterate value you are likely to get more choke if your bandwidth cannot handle it. Also, with a lot of players in the game world which means more data being sent you will also receive more choke (if your bandwidth cannot handle it). Finally, with a low rate setting, you also get more choke.
If choke is in effect, the server tries to see if it can send a packet to the client on every frame thereafter, rather waiting for the next multiple of 1/cl_updaterate, until the choke is gone.

Interpolation
The way the Half-Life engine uses interpolation is to store positions and times, when those (in game) positions were accurate, in its history. It then uses ex_correct to parse through the history for the best two positions (note that this does not have to be the two last positions). This means that a player moves at the same speed (the actual speed the player moves between those positions on the server) between its positions no matter what ex_interp value is used (as long as ex_interp set to 1/cl_updaterate or greater).

The only case when the player might move faster is after a huge drop of packets or if the player is under a great delay (because of latency) since he then is behind the game world and has to move fast into his correct position.