Ah... hadn't thought about different pixel dimensions and the effect they will have on my final results!

Sizes I have are:

2816 X 2112
2816 X 1872 (3:2)
2048 X 1536
1600 X 1200
1280 X 960
640 X 480

Quality settings are:

Fine
Normal
Economy
Tiff

Each image size can be saved at any of the quality settings giving me a possible 24 size/quality options!

I was all set to compare 2816 X 2112 fine and/or Tiff with 640 X 480 economy, ie. the best available with the worst available.

Now I'm thinking I should be comparing 2816 X 2112 fine AND Tiff (good idea to compare both Tiff and fine Gary - thanks) with 2816 X 2112 economy and ignore the smaller image dimenions for this exercise?