Rob Burrowes,   The S5100 series cannot run anything 10.5.x, and as far as I know there are no plans to change it as it is reached end of service. Now the S5100 will go to 10.4.3.6, or if they make another 10.4.3.x version depending if they find enough bugs/issues in which case they update the 10.4 branch again.
I do not see the S5148F listed as being supported by OS10.5.1, but it is mentioned in the release notes under known software behavior for 10.5.1 i.e. Bidirectional forwarding detection (BFD) is not supported on the S5148F-ON switch. So are these switches able to run 10.5.1?
Does OS10.5.1 work on a S5148F