Inspec and Microsoft Windows Audit Slowness

I have been working with Inspec for weeks now and one thing I have noticed that while its agnostic with most platforms out there (Windows, NIX), writing Windows audit code poses a challenge - speed.
So for general audits like file, directory, registry etc audit resource do a good job but when it comes to specifics like a particular configuration say in IIS (example checking for double encoded requests or HTTP header) I am still using PowerShell script (Get-WebConfiguration etc) and then using PowerShell resource to invoke the script. This is good because PowerShell is a powerful tool but it reduces the overall speed of running an audit check.
Is this something most Inspec engineers face or is it something that can be mitigated by using custom resources? Custom resource don't look easy to me.

Are you using the latest versions of InSpec? There were some significant speedups in the 2.x versions.