Turns out I must have gone about the original array a bit shonky. Started from scratch, doing exactly as I believed I had done before and things are considerably more speedy!

Currently using vCenter converter to shift the VM across, it's going along rather better. Only getting 30-40MB/s at the moment but that's as it's grabbing from an iScsi datastore about as far away from everything as possible. Hits 100 from the other array thankfully.

Cheers for all the input