Above those technical endless and useless threads, the so called AFE always quilled a bit the IQ of previous DP cameras. Always, I wonder why SIGMA implement it because it is always in BAD than GOOD for the final experience.
In +, on DPreview, most of the posters do not have used a vast range of those cameras so they just show up with speculations, falls conclusions yadi yada. Most of them own ONE DP, or ONE Sd but never invested a lot in the brand. Only few did it; I might had we are not on lot on the whole planet having owned and used extensively almost all SIGMA catalogue.
That mean, having owned all DPs and most of the SDs, that there is a drastic difference between non AFE and with AFE models. For example, the original DP2 IQ was just amazing (and still). The DP2s too, with better AF. Then came the DP2x incorporating the AFE from the SD15. Like the SD15, it is clipping highlights paradise.
The Quattro is using an AFE >> clipping highlights paradise.
The Quattro is the first digital "new" camera who incorporate AFE since the start. Habitually, Sigma kill the model with AFE crap by incorporating it in the second generation body, but here >> you got it from the beginning
So, never buy an "AFE" version of any Sigma camera. They got it wrong and still get it wrong in all ways.
None of the Merrill have AFE, and IQ/DR is flawless.