Hot on the heels of finding that
Yellow Button For Channel's +1 Version shortcut the other day I've found something else by accident.
Maybe it's been there for ages but since people keep arguing how much space recordings take up on their VM Tivos I think it's not well known.
To find out how much space recordings take on your VM Tivo V6 (not sure about old VM Tivos but probably the same I'd guess):
My Shows>Select Show You Want & Press OK>Press INFO > Scroll Right Down To Bottom (as all those I've tried have been off screen bottom) and right below "Categories" is "Disk Usage".
It reads like
Disk Usage: Less than 1% (4.58GB)
The above example is for a 1h30 film in HD on Film4
Another example says
less than 1% (1.71GB) and was for a 1h55 animé film on Vice channel.
Anyway, hope this helps everyone.