I have tried to upload a similar file and it worked fine while uploading, but the rebuilt process was giving me problems. It may be limits with your server or security measures in your firewall, but there's no other reason not to be able to upload ~2500 small files to your server because that's basically what's happening here. Just keep in mind that handling a 5GB file with regular client-server applications such as XenForo might be out of the scope of the possibilities. Just keep adjusting your settings until you find a good place where the size of the file doesn't give you trouble.