hey sam keep your pictures to a max of 1024 x ??? or 900 x XXX
nothing wrong with a bigger picture, but dont forget also that resizing to those 2 resolutions helps sharpen and clean up the picture a bit.
plus it helps browsers to not scroll left or right.

i usually use 900 x XXX (its usually 900x600) as its small and you can still see the image clearly.

just keep a copy of your original large picture for printing.