Will a 5D give me inferior pictures

It's a lousy camera. Don't buy one. Honestly. Your pictures will be vastly reduced in quality. (Take backups too - it might even pickle the ones you've already taken, out of spite.)

http://www.usa.canon.com/

Yes. Poor image quality is why so many wedding pros use the 5D. Why waste a good camera on weddings.

On a slightly (and only slightly - I still think it's a silly question) more sensible note, you may lose some by capturing image at the edge of the lens's design, the 5D has larger pixels than the 40D so it tests the lens less.

Honestly - there so much else that is going to determine the quality of your pictures, pixel peeping at the edge of the frame is about the last thing you should worry about.

"Will a 5D give me inferior pictures"
NO

Is the 40D enough for wedding?
... Yeah.
I don't thing there is (really) bad tools, but only misuse of the tools.

I don't think there is a general answer to this. There are several effects that one should inspect separately.

Center sharpness: Albeit crop cameras use the "sweet spot" of a lens, they are also (usually) more demaning in resolution (singe pixel density is higher on crop cameras) than fullframe cameras.

Corner sharpness: Since the corners on fullframe are further out of the center than they are on crop sensors, this might (or might not) become a visible difference. (It depends on the ratios of the pixel densities and on how much corner sharpness is worse than center sharpness.

Vignetting: Obviously, fullframe suffers more than crop 1.6

Barrel/Pincushion distortion: Also, fullframe will suffer more than crop 1.6

But even if you compare the results of your 24-105 on both cameras, you are still comparing a different range of field-of-view now.

"Got a 40D but always thought of full frame. I've read that APS-C sensors take advantage of the sweet spot of "full- frame" lenses due to their reduced image circle. In the event that I acquire a 5D am I to expect inferior results with Canon's 24-105mm and 28-135mm lenses and my 50mm & 85mm primes as apposed to these lenses on a 40D. Thanks."

The "sweet spot" business is, in my experience, pretty much bogus. It is one of those things that is repeated as a fact but rarely checked by those who repeat it.

When I moved from crop sensor bodies to FF bodies there was no degradation in IQ and, in fact, in most cases there was an improvement.

However, if you think that switching formats will automatically create some _significant_ change in the quality of your photographs, there is a decent chance that you'll be disappointed - it isn't quite that simple. Depending upon what and how you shoot the 40D OR the 5D could be the better camera.

Dan

I went from a 40D to a 5D and now I dont use my 40D

I'm disappointed Mr Atkins. I've never found a good lens that I could use for wide-angle landscape and portaiture with my crop cameras. One of the tempting things for me about a 5D is the thought of a 24-105 on it. I've tried various lenses (like 17-85 USM and a host of others) on my 300D/350D/20D/30D/40D as I upgraded cameras but was always disappointed with their sharpness and contrast. The 17-55mm is an option but I'm not going to pay almost $1000 for a non-L dustsucking trombone.