DSLR IQ versus Micro 4/3

I am considering purchasing a Canon 550D or Canon 600D which would replace my current Lumix G2 and I was wondering if anyone here had moved from Micro 4/3 to an entry level / mid range DSLR and had noticed a marked improvement IQ across all areas?

I know the Canon and Nikon DSLR's especially tend to be better at the high ISO range tending to outperform the Micro 4/3 range but I wondered if even at the lower end ie 100 - 800 ISO if users notice an improvement to the IQ because of the larger sensor?

I guess I am looking to tap into your experiences and any comments / advice is much appreciated

Thanks