Hi Nigel,
Currently there is no equivalent of the content drill down report
through the API.
For small date ranges, you could pull all the pages and do your own
roll up.
For larger date ranges, I think your filter method might be the best.
What you can do is instead of requesting all of the rows, just return
1 row and use the data feed's aggregate table to request the totals
for the matched metrics. This saves some bandwidth, but still you need
to go through each row.
Otherwise this is an open feature request. If people want this, let us
know.
Cheers,
-Nick