While going through various sources that give a quantitative measure of a lens's optical performance, I noticed that there is some significant discrepancies not normally noticed for other lenses. For example, a] PHOTODO rates the non-IS at 4.3 which is higher than the IS version which is rated at 3.4 b]PHOTOZONE, however, in their performance based on multiple inputs rates the non-IS at 4.78 and hence lower than the IS version [a whopping 5.13] c] PHOTOZONE'S individual sample tests also confirm the multiple user survey both as regards MTF[resolution] and chromatic aberration i.e.,the superiority of the IS over the non-IS version. Whereas for most other lenses there is a good co-relation between PHOTODO and PHOTOZONE quantitative lens ratings, the ratings for the Canon 300mm f/4 L IS and non-IS lenses is a bit puzzling. Is it a case of apples versus oranges comparison or quality variations in individual samples? Any comments from forum members please? I wonder if someone has come across references to actual comparison shots for the 2 lenses that could clear the confusion to some extant.