I'm sorry but I may be misunderstanding your thread here. You DO have videos on all the big tubes with millions of views, yes? Then you ARE 'monetizing' big tubes already. (I am assuming there are links, watermarks and banners on your videos.)
Now if you mean the various adshare programs these tubes have then I can understand your point. For me and my sites I find a combination of both works well. In other words, sending out smaller clips (6-8 minutes) and the occassional full length video.
Of course only you can decide if the additional exposure and video lengths will help or hurt your sites but I suspect longer videos will only help.
