Sorry for the lack of response on this - I have been so busy lately this project has got delayed due to more important commitments.
At this stage I think the FDR vs. FDR10 answer is the most likely solution...
How would I go about confirming the switch model from the software utilities. I can't find the above model numbers on the switch anywhere (its second hand)
Also I was under the impression that the SX600xx switch family were all based on the SwitchX-2 based hardware which could all do 56 Gb/s per port.
Is there a firmware upgrade we can use to increase the speed from 40Gb/s to 56Gb/s?