Dear Marcus,
I am surprised that, after a while, you are not acquainted with the forum 'Manage Attachments' features, placed in the the 'Aditional Options' section, when you submit a post.
Haven't you read this:
http://www.vikingsword.com/vb/showthread.php?t=14688.
You will find that the pictures size allowed is the most convenient for a full screen.
If anything wrong, just tell
MVG