Resolution of saved jpgs

[ebergerxn]

I am trying to determine how to save jpgs with an appropriate resolution so I lose no detail, but without blowing up the file size. Attached is my Save As/Options settings for saving jpgs. I did the following experiment. I did no image cropping; I just saved the images with differing quality settings.

I saved a jpg that had modest resolution - 450 KB. I saved it with Quality settings from 85 to 100 in steps of 5. This resulted in file sizes of:
orig = 450 kb
85 = 60 kb
90 = 77 kb
100 = 251 kb

I then did the same experiment with a large file of 1.2 MB and got
orig = 1.2 MB
85 = 1.3 MB
90 = 1.7 MB
100 = 3.4 MB

I was hoping to find a setting that I could always use that would be the optimum when cropping an image, to preserve image quality. For the small image I noticed image degradation at a quality of 90 and even the quality 100 setting did not save the file size, it shrank by almost 50%. For the large image, there was no loss of quality even at the 85 setting and when I used 100 the file size more than doubled. For the small file a setting of 90 looks good and for the large file 85 would be best.

Thus from my little experiment it appears that each time I save an image I would have to experiment with the quality setting for best results. I am wondering is a safe setting that I wouldn't have to check each time would be 90.

Also, have any of you found a setting under Tools/Settings where this could be set for all save-as operations instead of having to check it each time? Apparently it stays where ever you have selected for the last save-as operation.

Is anyone knowledgeable enough about jpgs to explain my observations and make any suggestions?

Thank you.