there's no need to resize images unless you want to for your own use. leave 'em big, it's really OK.
for my personal use, i resize most images to 1024 wide, sometimes smaller to 800 wide. this is just easier to deal with on my computer - i have no need for images that are thousands of pixels wide, who could even look at them, they're 5 to 10 times wider than the screen they're viewd on.
the only problem with trad gang resizing is if the image address begins with "https", which just needs to get changed to "http" before posting.
*HOPEFULLY* (please please, dear God!) all this imaging craziness will be put to bed once the new forum software is effected (hopefully this year, there are SO many damn hurdles to get over with the damn conversion!).