http://www.victorboyko.com/pmlag.mov
you will see what i am talking about.
I watched your movie. For some reason it took more than 30 minutes to fully load.
Your images are from a D200 and they are 10MP, not 8MP. Your memory cache is set to 256 MB of RAM. When a single 10MP image is loaded and is ready for display it consumes 40MB of RAM. Since your cache is set to 256MB this means that only six 10MP images can be held in memory at the same time (256/40).
In your movie you do not flip back and forth between two images, you perform the following sequence:
019, 023, 028, 031, 037, 042, 048, 052, 056, 065, 069, 074, 080, 086 before going backwards through the following sequence:
080, 074, 069, 065, 056, 052, 048, 042, 037, 031, 028, 023, 019, 014, 007 and then you go back up through the following sequence:
014, 019, 023, 028, 031, 037, 042, 048, 052, 056, 065, 069 and end the video.
A total of 16 unique images, using a total of 642MB of memory.
I note that it takes two seconds to load the first image (017) at 100%. Given that time, and the fact that Photo Mechanic works on four images in the direction you are moving, it would take about 8 seconds to load and cache the four images that you would then be able to zip through at high speed. But because you're whipping through the images so quickly and your memory cache is so constrained, Photo Mechanic cannot keep all of the images in memory at once.
I also note that in your usage pattern you never pause for even two seconds to look at an image so PM doesn't ever get a chance to finish loading a single image before you tell it you don't want to look at that image anymore and that you are now interested in a different image.
My suggestion would be to increase the amount of RAM in your system to 2GB and set Photo Mechanic's Memory Cache to 768 MB of RAM. That will help a lot and will keep a fair number of images in memory at once, but you'll still need to slow down your pace a bit. In your video you spend 27 seconds zipping through your images, visiting a total of 41 images which when there isn't enough memory to hold them all would take 82 seconds to load them. And when you have enough memory to load the 16 unique images, it will still take 32 seconds to load them. You spent 27 seconds going back and forth which just isn't physically enough time to load them on your system.
My additional advice would be not to go through the images at 100%, but instead use the non-zoomed mode and then Command-click on the detail area you want to see which will zoom that individual image up to 100% when you need it. Command-click again to return to non-zoomed mode.
As for your comparisons to iView, are you certain it is showing 100% previews? And as for ACDSee, are you running it on the exact same system? Or is it on a desktop system with faster hard drives and more memory?
HTH,
-Kirk