I'm not a photoshop guy but just how long does it take then ? Are we talking more than a few seconds here ?
Found this article today while doing some work related photo manipulation for a brochure. While it didn't address my need I thought you might all find it useful and the website looks pretty good as well.
Photoshop Cartographers: Want Shorter Draw Times? Try Bigger Tiles.
For multi-gigabyte files with lots of layers and effects PS can take a while to redraw (I've had 10+ seconds for a big file with around fifty layers, each having effects). PS was designed to try to do tiles that fit into a relatively small L2 cache and to ensure that the user saw something happening regularlly during processing. Processing and updating lots of small batches is less efficient than fewer bigger batches, especially when transferring data to the graphics card via the older, slower interface. The newer versions of PS are getting GPU accelerated so it's not as bad as it once was.
The whole article scares me in that it tells me how little I know. I don't think I'll dabble on this score lest I totally screw something up out of ignorance.