You should be able to get such info using the Get-Stat cmdlet, like:
Get-Stat -Entity (Get-Cluster myCluster0) -Stat "cpu.usagemhz.average" -Start (Get-Date).AddDays(-7) -Finish (Get-Date) | Export-Csv -NoTypeInformation c:\temp\myClusterInfo.csv -UseCulture
That grabs the average usage in MHz for the given cluster for the last seven (7) days, and exports it to CSV. You could adjust it to get that info for all clusters, or just certain clusters, or whatever you please.
That do it for you?