Good news!
I’m pleased to say I bit the bullet and upgraded to Windows 10 today and I have 7GB of cache and my PC seems just as responsive as it did under Windows 7.
Of course, this doesn’t help anyone who is stuck in Windows 10 with a non-working ReadyCache.
I had previously tried to get RC working in Windows 10 by installing/reinstalling & registry cleanup etc but in the end reverted back to Windows 7 using Windows 10’s “Go back to Windows 7” option until a fix was reported to be ready. This might be a route for some of you to consider.
Sandisk - shame you didn’t test with the Windows 10 before the release date so we didn’t have to go through this - but well done on getting a working fix out now.