I had the same question a while ago and SW support confirmed that it is not possible to report on Clients. Seeing who your heavy hitters are in a report would be nice.
I also brought up this request / idea. I was puzzled that WHD won't offer this, because I thought this kind of reports are obvious to create a proactive service environment. Maybe Solarwinds will add this feature / report into the next version of WHD.
this is a known feature request, we currently track this under #353007. I added your request to the record as I'd really like to have this kind of report, so as soon we are getting closer, I'll let you know!