Try the metrics.log. During each metrics dump (every 30 seconds), the "top X biggest Y" are written out. Where X is defaulted to ten (10), and Y is sourcetype, host, index, etc. The search string would read like:
index=_internal source=*metrics.log group=tcpin_connections | stats sum(kb) AS kb by os
You could also use the results from the os field in the tcpin_connections, to evaluate the OS while getting the accurate license usage from license_usage.log.
could you break down the search to specify heavy hitters by host build using a particular o/s (eg windows)
Yes you r right. I am assuming licensing usage by operating system, split down by hostnames which has the os installed.
Assuming you mean license usage?
You could tag your hostnames with the OS, and split your query by that tag. Alternatively, you can do the same with a lookup.