I can see the improvement, but I'm not at all sure it's worth double the file size.

I want to thank everyone for your feedback. I think I'm leaning towards 135 dpi with medium compression. But the 150 dpi medium sure makes a nice looking image for only a couple extra K. I'll look at the thumbnail approach, but that consumes even more disk space, and adds to the maintenance cost. One thing I don't like is a page with lots and lots of big images that takes forever to load, especially when the chip I want to see is the last one to load. I think the trick is good text-based indexing, but we'll see. This thing is still in the early concept stage.