Brett,
We've been trying to use Jmeter with some of our internal services and have had trouble. We think we're handling the https portion correctly but still get errors. I can post back with the specifics if someone would find that useful but perhaps there is another example out there for secured services? I too really like tereshenkov's blog.
Has anyone used System Test to test service loading?
https://www.arcgis.com/home/item.html?id=a269d03aa1c840638680e2902dadecac#!
MXD PerfStat is what ESRI Professional Services would use.
The tool to do that would be System Test for the Web.
https://www.arcgis.com/home/item.html?id=e8bac3559fd64352b799b6adf5721d81#!
This is an Esri PS tool.