Walter,
I know it's only a typo on your part, but just so Gracias doesn't get confused...
It's 20MBps (MegaBytes per second) and 30-40MBps, not megabits per second as the lower-case 'b' in "8bit...20mb/sec" implies, for 8 and 10-bit UC. e.g., DV/DVCAM is 25Mbps.
Gracias, download the AJA Data Rate Calculator to determine size and data rate for a wide range of formats. Be sure to open "Preferences" for details on Binary and Decimal measurement.
http://www.aja.com/support_Io.html