I have just purchased 2 x CRS326-24G-2S+ and connected them with a 0.5m SPF+ DAC and assigned IP's to the interfaces on both side and run the bandwidth tool, but I only get 800-900Mbps

is there anything obvious i am missing?

Bandwidth test itself is a resource-intensive operation, while CRS326 is not very powerful CPU-wise - try testing through the devices, not from one to another.

Thanks I don’t currently ether ability to test through as this is the inter connect between the two only at the moment, I can see the cpus are maxing out so this must be the issue