Hi Reyalp,
Thanks for your thoughts. The fact that not all DIGIC IV processors are equal is a little surprise for me, I really thought they were.
Please understand I said they are not
necessarily equal. The main factor here, which we know for certain, is the sensor is different, and these sorts of high frame rates are usually associated with CMOS sensors. The sensor is not part of DIGIC.
Regarding DIGIC, I don't know for a fact one way or the other. I wouldn't be surprised if Canon "bins" them like CPU manufactures do. It would also make sense to have different clock speeds because of thermal limits (A DSLR has a lot more cooling capacity than an ixus). Variants with less cache, different bus speeds etc are also all plausible.
ISTR Canon has said the DIGIC in P&S cameras is the "same" as what is in DSLRs, but what this means in marketing speak isn't necessarily what it means to an engineer
In my understanding, available readout modes are ultimately limited by the sensor (although there could be secondary limits like bus speed, RAM speed etc.) So even CCD cameras with the same DIGIC chip can have different hardware limits for frame rate and resolution.
