pbase does seem a lot quiter than it was only a year ago, true. However there are still some good and very helpful folk on here (Dang, DougJ, DJWixx, Prinothecat, Toosnvetts, Sheila Smart and plenty more) who post regularly and give sound advice. Not like on DPreview where all people seem to do is have "bun fights" over meaningless topics
For what it's worth, I've got a 5D and the images are generally fantastic. Not perfect but very very good indeed. I moved up from a 20D but also kept it and use that body for wildlife efforts, which it handles well apart from the very noisy mirror reflex! I use three lenses - 17-40L, 24-105L and 300 f4 IS L + a 1.4x converter when needed. My only potential problem is if the 5D body goes down then i can't get wide angle interior shots done on the 20D currently. When I can afford it I'm after a Sigma 12-24 so I can get either mega-wide or decently wide depending on the body it's on.
I met a guy with a D300 the other month and I can honestly say it's a great camera - you won't be disappointed! I wish Canon WOULD change the way their bodies operate, personally. They're just not (to me) intuitive to use like a Nikon is. I still can't get the hang of shutter and aperture wheels swapping function between fully manual and Av or Tv modes. I realise it lets the control wheel handle compensation but to me it's just not logical. I can't be doing with the top panel adjustments either. Even a few years into Canon I can't remember which wheel changes what and wind up wasting time remembering. Of course it could just be ME but I am usually very handy with technical stuff (you should see the Yamaha A4000 sampler I have to operate in the band I play in and I've got that well sussed!) . I also never have such problems when using Nikons (or the K-M 7D I used to have, which was a joy to use). Ultimately, though, it's about the images that people get to see and the 5D does that bit particularly well! Can't vaguely afford to switch to a Nikon D3 either!
There's also for me the fact that the 20D is my late Dad's old camera so I have more than one reason to be using it!
The things I like about the 5D are the big viewfinder (makes a massive difference in practice and you can actually use the DOF preview again), the size and weight (I like 'em big and weighty, personally) and the high ISO image quality which is just superb. The tonality of the images is lovely too, unless the light is flat - then it just blocks up the colours but then most digitals do that.
However if you need fast and accurate AF then i'd certainly go for the D300, especially in lower light. The 5D is by no means bad but it does get a bit hit and miss when the light drops off.
Having said all that, what do you think you'd be missing out on by buying a 40D? It's a bloody good camera!
What size images do your clients require? I'm sure it's more than capable isn't it? You also have the advantage of being used to using Canons.......
Don't worry too much about weather sealing unless you're out in downpours a lot. My wife used my 20D in the rain at a gig the other month and it's fine! Obviously she covered it as often as possible.....
Be very careful not to get swept along in the "must upgrade, must upgrade, must upgrade" current. I used to feel that about my 20D but then I started using it with 'L' lenses and realised how good it actually was! I'm still using it now, I'm making shots for clients with it and it's more than up to the job. The marketing departments at the camera companies must be the busiest in any industry at the moment - just look at how they push megapixels on the compact cameras when all they're really doing is creating noisier images. People could have used a 6mp or maybe even a 4mp to generate the images they view on screen and print 6x4s of and actually would have got cleaner pics!
hope some or all of that proves helpful!
Dave
PS something that just jumped out from my memory: The other year, a TV programme over here gave top (and I mean top!) landscape photographer Joe Cornish a challenge to produce a decent landscape from a mobile phone camera. He found it a bit frustrating and certainly challenging but when I saw the pic he'd taken I was very impressed to say the least. Now that of course is extreme but don't forget in all this current world of "must have" that it's the PHOTOGRAPHER who makes the image what it is. The camera is only a means to an end. Ansel Adams was knocking out stunning landscapes in the 1920s on gear that most of us wouldn't even consider using. And there are great sports photographs from the 60's, 70's, 80's etc arent' there? Just a bit of food for thought (for me as well!)