I have two questions regaring IQ (nothing else):
1) What are the main benefits of a larger sensor regarding IQ?
2) We take 2 pictures, one with a ASP-C dslr and one with a m4/3 camera. Same picture, same lens, same ISO of 100
   A) What will be the difference ?
   B) What will be the differnce on a small print-out (for exemple 20x30 centimeters)

APS-C will be in theory marginally better, because of the larger pixel size. The difference is about 20% for the same pixel count, because of the different aspect ratios.
In practice however results will depend a lot depending on which exactly cameras you compare.
For example K-r is much softer than E-P1.

I won't post an answer, instead ill post some samples later, I'll try to make it as  controlled as posible, manual focus, studio lights, you name it. Give me 2 hours or so.
Just for kicks, I won't post what shot was shot with what camera (that's part of my answer)

Anyone own an APS-H camera?

I could borrow one, it'll take a week

It's a weird size sensor, with an even weirder crop. But I think canons APS H 1d is phenomenal.

Its an interesting one and also one I'm sure a lot of us have thought about.

In a print as you mention, I doubt there would be a huge difference. In pixel peeping, there sure would be I guess, but I don't really consider that real life to be honest.

IMO it also depends on what subject. A brick wall for example, I can't imagine a major difference. However, on bird feathers and the fine details they hold I would not be surprised to see quite a bit of difference. Using the same lens that is and only a different sized sensor. Then again, that would also apply to APS-C sensors from different cameras as well. Tricky one.

Now thrown in a full 35mm sensor and its a whole new ball game

I have what I consider to be a "nice" APS-C DSLR....

However, since the purpose of this thread is to show that...."only idiots buy over-priced APS-C DSLRs".....I won't post any pictures...

Instead, I'll just call myself an idiot & call it a day 

not what I want, so here's my two cents instead of photos:
At ISO 100, its difficult to tell the difference between 2 good performing cameras. If there's lots of complex light and shadows, the 4/3s sensor might clip faster than the APS C. You could get the same result, but you'd have to put in a bit more work to get the highlight detail. I'm assuming were shooting raw. The difference won't be astronomical, not  noticeable even if you expose correctly, but if you look for it you'll find it. If you go all the way to full frame the jump will be tremendous, you'll actually have a hard time clipping a highlight.
I PREFER 4/3s output, to me its sharper and easier to work with in ps. So that makes 4/3s better TO ME. That doesn't mean 4/3s is better, APS C will always have the slight edge, its physics. It's a preference thing, I certainly understand panther's frustration.

At least Ive never had a client say HEY!! these prints are from 2 different cameras!!!That one is APS C and that one is 4/3s!!!

There is. I actually have a test prepared.

I have two questions regaring IQ (nothing else):
1) What are the main benefits of a larger sensor regarding IQ?
2) We take 2 pictures, one with a ASP-C dslr and one with a m4/3 camera. Same picture, same lens, same ISO of 100
   A) What will be the difference ?
   B) What will be the differnce on a small print-out (for exemple 20x30 centimeters)

In small print outs you will hardly see any deference that is up to A4 size and on your regular PC screen but anything bigger will be bad you will see the pixels and IQ will be down.
From my experience and knowledge smaller CCD has smaller dynamic range and this will effect on picture IQ.
I am using Canon 30D APS 8MG which is relative an old camera from 2006 and I can pull out some outstanding photos from it, the major thing is the lens the higher the quality the better its depends directly on how much one wants to invest on a lens chip lens has low resolution expensive lens will have good and better resolution designed in it so you will get much better IQ in your photos.
See my photos in my gallery: http://www.flickr.com/photos/yankl1/collections/
JD

Interesting. Definitely more DOF in the ASP-C version.
Thx for sharing !

Interesting. Definitely more DOF in the ASP-C version.
Thx for sharing !

Because the 50mm f/2.8 on a m4/3 sensor has the same DOF of a 100mm at f/4, so if the 100mm is also at f/2.8, then it will have less DOF... the f/2.8 has not changed, just the DOF because of the format size difference.

Which is why m4/3 (or any smaller sensor than FF) needs faster glass to achieve similar DOF.

Because the 50mm f/2.8 on a m4/3 sensor has the same DOF of a 100mm at f/4, so if the 100mm is also at f/2.8, then it will have less DOF... the f/2.8 has not changed, just the DOF because of the format size difference.

Which is why m4/3 (or any smaller sensor than FF) needs faster glass to achieve similar DOF.

Would actually be 100mm f/5.6

Another way to think about why FF sensors have low light advantage over smaller sensors with the same resolution.  Just like the DOF changes by two stops, the equivalent ISO setting has to change two stops on the camera, so running a m4/3 camera at iso 100 has the same noise as a FF camera at iso 400. Given the exact same sensor.... which it isn't... cause they're different sizes...

Which is why I want my focal reducer to work! boo.