Hi,
no, the 3TB HDD did not work. The iMac did not recognise the 3 TB HDD - if I remember correctly (it was a long time ago!) the iMac only recognised 640 GB. I exchanged it for a 2 TB Seagate HDD with thermal pins. BUT - that's Apple for you - it did not have the Apple firmware. So the iMac booted, worked well - for about 10 minutes and then the HDD fan went on full blast, obviously creating a lot of noise. The only work-around solution was HDD Fan Control Version 2.4 - downloaded from http://www.hddfancontrol.com. After installation, the iMac ran smoothly without noise pollution.
Since then I have changed to another iMac with a SSD (250 GB) and a HDD (2 TB), 16 GB RAM. The machine is so wonderfully fast that I am not even interested in looking at the newer iMacs, which would be so expensive in comparison with the iMac that I have.
I hope it helped. Nice hearing from you after such a long time.
Kind regards.
PS I hope Apple will not censor this posting.