Thanks for all the replies.
Not having either a Sony camera nor the set up capability, one thing is clear by the postings, there are differences, I was only aware off subjective differences when viewing the TX output when the SDX-900 was intercut with DSR 570/450. One large news broadcasters in the UK has changed over from DvcPro and SDX cameras to Sony DvCam with DSR 450, Must have been a political decision and not on technical grounds!