Thanks for all the replies.
My aspirations are in bird and aviation photography (but my photography is not limited to that). I already have some reasonable glass (not 'L' or prime but my wallet and SWMBO are not suited for such investments) - to list them:
Sigma 10-20mm f4-5.6 EX DC HSM
Canon EF 28-135mm f3.5-5.6 IS USM
Sigma 150-500mm f/5.6-6.3 DG HSM OS
plus a couple of less desirable starter lenses that kept me going for a couple of years until I could afford the above.
On account of the Sigma DC lens I want to stick to APS-C sensors. I want the upgrade to be in pixel-count as well as quality - so that I can afford a little cropping more than I can with the 8MP of the 350D - so this rules out older
XD models.
I'm coming round to preferring the 50D but holding back because of the higher risk in buying refurbished - is the saving worth it? If the 50D was brand-new at that price, I don't think I would have this dilemma.
The 50D comes with a lowly 90 day warranty and is described as
Manufacturer refurbished: An item that has been professionally restored to working order by a manufacturer-approved vendor. This means the product has been inspected, cleaned and repaired to meet manufacturer specifications and is in excellent condition. This item may or may not be in its original packaging.
Further on the camera is described as "REFURBISHED TO NEW CONDITION BY CANON", is from a UK seller, UK shipped and the full package includes:
* Canon EOS 50D SLR Digital Camera (Camera Body)
* BP-511A Rechargeable Lithium-ion Battery Pack
* CG-580 Battery Charger
* USB Interface Cable (IFC-200U)
* Video Cable (VC-100)
* Wide Neck Strap
* Eyecup Eb
* EOS Digital Solution Software CD-ROM
* Software Instruction Manual
* "Great Photography is Easy" Booklet
* "Do More with Macro" Booklet
* Free 8 GB CF Card