Yes, that's the problem. We just switched over to serving the static stuff off this server while we investigate. The extra load may make things here a bit slower but the site seems usable.
Is the change to 25 front page stories a temporary one, to help performance?
Yes. I tweaked several variables to decrease load.
Does HN run on srv.arc and app.arc?
Yes. The code I released is identical to the files on the server. Or at least to a snapshot of them in the past.