Ask on the ModDB or GSC forums - I think I saw something about this caused by ATI drivers but I may be wrong. Having an HDD (vs SSD) should not cause 5min saving times, an SSD is faster but even so, if you have 12GB of RAM then Windows is still going to cache a lot of the game files anyway. I played all 3 STALKER games on an old Q6600 with HDD and saving was always a second or 2 and this game still uses the same (but newer) engine. Plus the saves are not very large so I seriously doubt it's your HDD. If the game is pausing horribly when you go back to the menu then it's clearly a bug or possibly a driver issue.