I've been uploading my full hd camcorder stuff to youtube reencoded via Handbrake at a constant quality RF=20 settings.

The videos come out at a little under half of the original file size. Because uploading HD to YouTube is really painful via ADSL (1mb/s is my usual upload max speed) i just wonder what is the minimum file size required to retain the 1080p full hd setting on Youtube?

eg instead of using constant quality rf=20, using an average bit rate manually set. 5000 kb/s works, but how much lower can i go?