In reply to quiffhanger:
So, I tend to hang onto things in whatever way minimises force on my forearms. On small holds this is often with a bent arm (try it on the finger-board: hanging at your limit is harder, for me at least, with completely straight arms). Likewise, leaning right back on a sidepull, depending on it's position often feels more strenuous.
So is this advice body-type dependent or do I have crap technique?
Bigger built people with a higher centre of mass will naturally benefit slightly less from straight arm hangs on some moves, but i think its really move dependant. Having shocking technique myself I tried to answer your question by watching people with good technique.
In this video: at 1:20, Ondra rests with a bent arm on an undercut. Weight on his feet, which is better at this angle for these holds, as you suggested.
Watching videos, bent arms are the exception. Most top climbers redpointing hard routes (therefore usually climbing the most efficient way they can) chalk up and clip with a straight arm. The main difference is that they also pull their hips in close to the wall, keeping weight on their feet. In this video, Ondra's hips never hang away from the wall - no saggy bottom for him. I tried to find another example of Ondra or Macleod (technical masters) resting on a bent arm, but after ten minutes got bored. They rarely do it. Possibly because the stuff they are on is so steep. On more vertical walls, its obviously more likely to be more efficient to have a bent arm than on the steep stuff.
I watched your brookes features video again though, and I think I have a criticism - you end up doing inefficient/unbalanced moves because you insist on keeping two footholds all the time, rather than shifting to a more balanced position on one foothold. Just a thought. Not something you see from a technical master ; )