Pauls9 thanks for the tip, I enabled the extra columns but the problem is during the 'stall time' the Task manager window actually freezes for a time also.
I timed the disk thrashing to a little over a minute with no bytes at all being sent across the LAN from the machine (which probably explains the timeouts on Network locations on other machines trying to read from it).
I've re-loaded NIC drivers, swapped network cable, still stalls... <pulls hair out>