Whats the maximum speed for a cable modem's upload and download speed.?

There's really no answer to so general a question. It depends upon the provider and the system they're using. About the best answer to your question would be that Euro DOCSIS 3.0 8 channel offers a maximum of 400Mb/s down and 180Mb/s up. These speeds are in millions of bits per second. In theory, a cable provider could use something other than DOCSIS or use more channels and get a higher speed. If you consider fiber optic approaches (like Verizon's FiOS) to be cable, then the speeds get much higher. In theory, you could provide billions of bits per second if you really wanted to (although the customer would need a router costing over $20,000, so maybe that's not such a good idea). Verizon currently offers speeds up to 50Mb/s each way though 50 down 10 up is more commonly available.

It dependson how fast you type. The faster you type on the keyboard , that slows down the responsed from your computer, Everything else between your keyboard slows down the electricity (Bits) from the maximun (speed of Light) on down. In theory a Fibre(Fiber) Optic Network with High Speed servers could go to 400 MB/s but no human can read at that speed. Even the OLD style Ticker mschines from the Telegraph Co's Could only match 10 Characters per second.