said by Jerm:in reality the downstream channels can be placed from 57MHz to 999MHz if the cable company wanted to place them anywhere but they would have to have 1GHz gear to put channels higher than 861MHz. I know in my area the downstream channels are in the 780MHz to 816MHz range right now. said by prairiesky:
If a free channel became available, it's use is more valuable as a download channel than an upload.
Upload is generally 5-42Mhz. Downstream is generally 600-700mhz.
You can't just substitute one for the other... cable plants act very differently downstream vs upstream.