Here are some comparison shots with LIKE subjects. The 55~300 I do not have anymore so those pics were taken a while ago (well, not a long while ago maybe 6 weeks ago), today I went down to my beach with the 50~200WR and took the like shots. As you will notice, the 55~300 are more close up because of the extra reach. Here are the settings:
Lightroom (Import from RAW)
Adjusted exposure the same for all pics (I shoot under to avoid blown highlights)
25 Sharpness (as imported from camera settings embedded in RAW file)
1.0 Sharpness Radius (as imported from camera settings embedded in RAW file)
Cropped to 8x10
All shot at 200ISO
Exported @ 800px width, 300dpi
[NOTE: No need to post crops as the comparison is done as an IQ reference for screen and normal size print purposes.]
Marc is right, there is no difference on these screen images - overall IQ appears to be exactly the same across both lenses (@ 7.1, 9.0 and 11 apertures).
50~200 WR Test Image Set f/7.1 [115mm] f/7.1 [68mm] f/9.0 [180mm] f/7.1 [200mm] 55~300 Test Image Set f/9.0 [260mm] f/9.0 [210mm] f/9.0 [300mm] f/11 [300mm]