iMac 2017 3 TB Fusion Boot Camp slow Performance IO?

When running Boot Camp Windows 10 Pro on my new iMac 2017 with 3TB Fusion drive I suffer very slow and sluggish performance. It almost seems like it could be a driver issue but I am not sure. I have installed the Boot Camp support software and so that is all running. However very slow IO performance e.g I click the start menu takes ages to load very sluggish. Windows 10 is up-to-date - Mac OS Sierra is not slow at all. I used to have a iMac 27" with 1TB fusion drive and it did not suffer this issue.

Anyone else experience this issue have any suggestions on a fix or a starting point of where to look?

Thanks

Specs:

4.2 GHz Intel Core i7

8 GB 2400 MHz DDR4

Radeon Pro 580 8192 MB

3TB Fusion HD

iMac (Retina 5K, 27-inch, 2017)