[YouTube-API] orderby cache

I'm trying to use the API to deliver 'top 5' data results.
When using:

http://gdata.youtube.com/feeds/api/users/channelname/uploads?orderby=viewCount&max-results=5

The results are cached. How long does this cache run?
I know authenticating bypasses the cache, but only when not NOT using
orderby, as stated in this video:
http://www.youtube.com/watch?v=sOEAD-gfJ_M&t=6m30s

As far as I can see it, to get any ordering with up-to-date data would
mean pulling back every single video entry. This obviously increases
our server-side processing and user page load times.

Can anyone offer their views on the best approach for up-to-date
ordering?

Chris

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