All issues have now been resolved
I stopped messing about and moved the slackware box up the network
The result being that all network functions now seem to operate as expected
and I am a slightly wiser person
Just for the record
mii-tool checks out the belkin F5D5130-5 as FD
my conclusion is that it is just a bit pants
it sortof works but just not as well as it should
up-down traffic gives no problems
pity about the crosstown traffic
and it looks like belkin feel the same as they have dicontinued it
Many thanks for all the help