Reply to thread

Lets start with this.

Try resetting the preferences file.

It cures a lot of strange behavior in PS.

Start Photoshop and immediately hold down Ctrl+Alt+Shift (Windows)

or Command+Option+Shift (Mac OS X).

Then, click Yes to the message, "Delete the Adobe Photoshop Settings file?"

This probably doesn't apply but if you open images in ACR a slight sharpening "IS" added.

Also as I recall. the most accurate way to view your image is at 25%, 50%, 75%,100%, 125%, etc., etc.

 I don't remember why or if it's still true but check it out and see if it applies to you, either way reset preferences and update your video driver too.