4x10 seconds is good for mgp galleries. If you compress it right it shouldn't run to more than 4.5mb
However theres a lot to be said for big clips .ie 2x 30 second clips as used by movie galleries from the likes QMov who edit their shit perfectly (see here):
http://www.qmov.net/g5/509L/interracial_sex.htm
Those clips are like mini advertisements and don't give away too much but tease the fuck out of the surfer
Also see this article by Redshoe:
http://www.ebonytraffic.com/articles...atersales.html