Does is slow down page loading ? It is already at 6 seconds.
Hmm, 6 seconds isn't good nor is it bad. Where are you getting this number by the way?
So yeah, it just depends really on what you're trying to accomplish. If you optimize delivery by compressing the image and using a CDN service (optional), you should be okay. Make sure the image isn't huge or more than 2000px in size. Remember the larger the image, the longer it takes for the end user to download.
When "community.nodebb.org" was updating, nginx servered a "502 Bad Gateway" text error page instead of a custom page displaying something like: "We will be back soon". I recommend that NodeBB creates a static page that is directly servered by nginx when NodeBB is down. This page should use the exact same theme as you currently have selected for your site. I think the link to nginx should be automated as much as possible (maybe ask [yes]/no permission in setup). But if it can't be there needs to be an easy tutorial on how to link nginx to this static page. The static page should be able to be overridden. It should be updated every time the theme changes. Thoughts?