Solved Windows 10 April 2018 Feature Update audio glitches and stuttering on old x58 system

This is a bit of a self answering post to save other people the troubleshooting that I've had to do.

I'm on an old system from Dell, where the motherboard and CPU are from an old Studio XPS 435MT.  It's an old (but still managing) Core i7 940 CPU, but the bigger challenge is the ICH10R SATA ACHI / RAID controller.  

To cut a long story short, after upgrading from 1709 to 1803 (via Windows Update), I got horrible audio stuttering on both the built in Realtek system, and an external Focusrite Scarlett 2i2 (2nd gen).  The fact that I had problems on both made me think that the issue was more fundamental than an audio driver issue, and so it proved to be.

It turned out that I had horrific DPC latency issues on what Windows had defaulted to as a storage driver (storport.sys).

After digging a bit, I installed the latest Intel RST driver.  No joy. It was just as bad.

Then I realised that Intel probably dumped support for ICH10R donkey's years ago, and so they did. In fact, they seem to have dropped it back in 2012.

So I uninstalled that, and downloaded Intel RST version 11.7.0.1013 from the Intel download site (thankfully it is still there).  This is the last version of the driver with support for ICH10R as far as I can see.

After installing this version, the audio problems are gone, or as good as gone. The latency on storport.sys is nominal again.

I just hope saves someone else the troubleshooting nightmare. Intel have left us poor people that are milking the last life out of the first gen Core CPUs high and dry with regards to Meltdown and Spectre patches, and the performance has been badly impacted by few patches that have released... but at least this might let us keep the old ICH10R chugging along a bit longer!