Images appear different betwen PS CS3 and CS4: Why?

My G5 Quad running leopard has both CS3 & CS4 installed. The same file opened at the same time side-by-side on the same monitor looks different why?

I've triple checked the the Color Settings (which btw are identified as being synchronized). Is there a known difference between the two generations of PS?

The stranger thing is there is no pattern of relative rendition: depending on the particular file, sometimes the image will appear less saturated and less contrasty on one version of PS, sometimes onthe other. All files under scrutiny are processed from RAW via LR into ProPhoto RGB space, which is also the working space in both generations of the Ap matches.

Is there a way to have the two versions render the files the same appearance?

Aaahhhh . More information. I m running 2 displays (Lacie 319 & Lacie 324). Main (for my critical viewing is the smaller more accurate 319 with highter bit LUT. 324 is wide gamut and does not calibrate well. Note my start-up monitor (the one with the menu banner inthe topI is that larger secondary monitor however. Also, I see there is one key difference is behaviour between the two versions of PS. In CS3, dragging and image between the displays caused their appearance to visibly change as one might expect given the difference in calibratablity of the two devices. I presume the file references the Display profile via Colorsync for which ever monitor that the file is open on. However in dragging a file back and forth between them in CS4, no marked change occurs. Which leads me to wonder, which ICC Display file is CS4 referencing for its display of the file?

Has anyone any insights here?