Canon SD550 of SD600?

[who_am_i]

Hi!
I'm mulling over these two and I just can't seem to make a decision which one should replace my Ixus V2
I need a super compact with decent quality and was inclined to buy the SD600 as it is newer and much smaller than the SD550.

However. I generally always shoot my pics at the manual setting, using the lowest ISO (50) even if it means using a minitripod or setting the camera down on a table or something. I do this because I hate digital noise.

Reading the review here on Steve's Digicams about the SD600, I had made up my mind at first. But then I saw the sample pictures.
Unfortunately they were al taken on the "auto ISO setting", so there's no way to check what ISO was used. (In the EXIF data it also just says "ISO: auto")

But I found it terribly off putting that the ambient light photos from the SD600 were so terribly noisy.

(?) What I really want to know is how the ISO 80 photos of the SD600 compare to the ISO 50 photos of the SD550. (I've seen the sample images at the Canon site, but I'd rather trust a first hand experience.)

(?) Also, the SD550 has a physically bigger sensor than the SD600. Is this an advantage over the SD600 at all in the pictures?

Thank you!