So Colin, has that cleared things up for you? 
I'm in much the same boat <no pun inten... well maybe alittle> as you and I'll share my own opinions for FWIW..
I'm looking to buy two set-ups, one for me and one for my wife. Cost becomes a bigger issue in my case and I can't buy anything yet as I'm finishing funding an MBA. I've been through the spectrum of choices, drooling over the D2x in the Subal housing, spending hours on the web sites of the manufacturers listed above and I've kind of come down to the following criteria.
How good a photographer am I? - answer is not at all. I've enjoyed my Sony P9 but am annoyed by the limitations of it..
What do I want to do with the prints? - In my case, I'd like to print out to 16" 20" and put nice pictures on the wall in my house.
How many megapixels do I really need to do that? Common concensus seems to be that 6 will do that job quite nicely. Goodbye reason why I absolutely must have a D2x :angry:So probably Canon 20D or D70. Further conversation on here seems to indicate the extra 2 megapixels probably won't make that much difference for my requirements in comparison to the £300 or so x2
What will affect this? Seemingly the optics of the port, but how much? seriously if its in focus its going to be a big bonus - there are definitely guys on here that will notice the difference, but will you? Will your friends? Spend the money on the lenses, this is where the difference will be made through better and faster focussing and of course quality.
What do I really need from a housing? It needs to be rugged enough for me to take on holiday, oh and look good
. - There's plenty of people who do more than that with the Ike housing and it appears to do a fine job (incidentally, naming Ike and the polythene bags in the same sentence was a little harsh!!).
Am I going to make money from my photo's? - almost certainly not.
Finally, many people here have their setup in their signature. Find someone with the various setups and see how much difference you see in the photo's. If you see lots then you're going to notice with your setup - if you don't... (incidentally, stay away from the guys with a D2x! <_<
I can't remember who's site it was (helpfully) but someone here has great photo's with the Ike housing and D70. That was enough for me (well, today anyway)
Come back to the basics... What do you really need.. What's your budget and will your requirements have changed that much in 2-3 years.
Hope that helps in some way.
James