There are some differences for sure, Flickr doesn't allow you to import images directly to an Album like Photobucket did, you do a general import from the front page and then select the images you want to put in each Album. Better in some ways, one picture can go into an Album and it's only on the drive one. Less convenient it that it's an extra step in the import process which is less than fool proof.
But, I've start doing my files at 2650 x 1600 for full screen display. Probably a mistake, I should have gone to a 4k display size in anticipation of my next computer.
Now when I post a photo on the forum
If you click on the iamges you can see it in original size I uploaded it. Or for my own use, I can click on a slide show, put my browser in Full Screen and click on the arrows in the right bottom corner to have a full screen slideshow, ruined only by the browser's menu bar. Pretty cool,
I've actually wanted to do this for a while. I thought if I waited long enough Photobucket would increase their size limit and slow down their ridiculous IQ degrading of uploaded files. It's all moot now.
If you have alarge screen, go ahead, click on the photo. If you put your browser in full screen then click pn the right bottom corner arrows, it should pretty much fill you screen.