The SD1 actually DOES stand up to the 645D!!

Have a look at this RAW comparison based on the files from Imaging Resource.

I have improved the processing further, no tricks.

Although the 645D is slightly better in some texture areas, I do think the SD1 can truly be called a 45MP 'equivalent' camera. I'm surprised myself, to be honest.

Be sure to click 'original' so you can magnify to full size:

I upsampled the SD1 with Spline Max 200% because all upscaling works better in such increments.