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I have added on my website the topic - How to make a lag free Counter Strike 1.6 Server and many people have found it very beneficial especially the low bandwidth users.
First of all to make a good 10 - 12 slot server, 512 kbps is recommended upload speed.
Even if you have 256 kbps upload speed, you can manage to create 8 slot lag free server. (if you increase the slots to 10, the players will be seen framing to manage the lag, server will send less updates per second)
Click here. All the steps has been described in a systematic manner. All the server rate information like sv_maxrate, sv_minrate, sv_maxupdaterate, heapsize, etc.