According to a steam page i read once the rate depend on how many slots on server, 20 slots or less you can set rates to 30000 over 20 slots 25000, the cl_updaterate and cmd_rate should be set to the tick rate of server, tbh i have my rates set to 30000 all the time, the server what you connect to ultimately sets the max rates you can use.
It's been awhile since i thought about rates etc, please correct me if i am wrong.
Cheers Trippy