What is the optimum picture size for upload?

While I know your 'program' resizes larger pictures to fit the CC format, those of us who have the capability of 'resizing' large pictures could greatly reduce up-load time, especially when our original pictures are 20+ meg each, and we want to upload say 300 or more reunion photos. {I anticipate doing a large upload again after our October 2015 reunion}
Delivering the images to you close to the optimum size will reduce upload time.

Excellent idea.

Been some time when I tested this. This is what I can remember.

Assuming you mean for the Galleries, it's 1000 wide and 800 tall (or so). Gallery system resizes images (per img size tags - not the actual image) to fit on a screen. So you can have taller than 800 and gallery system will autoresize at the expense of the width (it gets reduced in viewing)..

Easy to verify above - just upload one big one and see.

Reducing them in size ahead of time can save 1/2 of the file vault space used Set the compression value on whatever program you use to about 50% - depends on the program - and play around.