Honestly? It just depends upon the particular time/experience.
I tend to have two types of orgasms and I don't mean based upon where they come from. I have the frantic, rushing, "OMG OMG OMG" orgasms that are exhausting and mindblowing and I can have several of them at a time (10-20) over a 30 minute period.
But then there are the "ahhhh..that feels nice" kind that I've been having lately. We just got a G-Ki and have been using it with a bullet on the clitoris. Once I get started going - I can have 10-20 in about the same time frame but they are more...quiet...relaxed (sorta). My whole body doesn't shake but my torso does. For some strange reason - although they aren't as powerful physically, they feel more powerful emotionally as my man will hold me and whisper in my ear about how I can have "more". He's really good about sensing when my body is ready to stop and never over-pushes me but he also encourages me to keep going longer sometimes when I'm feeling overwhelmed.
I'm not sure that I'd want to extend what I have though - I mean its like a lot of multiple little shocks that make you jump but they feel oh so good. I think if they were longer it would be a bit more exhausting for me.