I have a 2009 27" iMac with 3.4GHz core i7 and 16GB Ram running OSX 10.8.2

I bought a 3TB Seagate GoFlex home NAS device and connected via a Netgear DG834G wireless router, using 100mb ethernet connection

When Time machine starts to backup to the NAS it reports it is backing up 650Gb of data and time remaining varies between 20 - 23 hours... but it has never completed a backup yet.

Previously I was using an old Iomega USB connected external drive and have been backing up to that successfully using Time machine since i bought the imac.

using the windows app "NAS performance tester" under a parallels VM it reports the Seagate GoFlex drive has an average write speed of 2.35MB/sec and read speed of 206.31MB/s.
the same app reports the old iomega USB drive has an average write speed of 12.4MB/s and read speed of 240MB/sec.

I would have thought the NAS would have much superior performance to the old iomega? any comments on what may be wrong here