This is speculation on my part, but I think even the daily activity e-mails are slowing the server down. Here's my reasoning:
Like clockwork over the last few weeks for a few minutes starting at 1am EDT I've been seeing really long load times on the messageboards. Usually in the range of four to five minutes to load a page. By 1:10 or 1:15 the problem goes away and usually doesn't come back. This is specific to ENWorld, because when it happens I always go check Google and an EZBoard or two to make sure my ISP isn't having problems.
I don't currently, but I used to have a few active threads set to daily notification. When I did, those notification e-mails arrived within a few minutes of midnight, again pretty much like clockwork. This however was before the switch to Daylight Saving's Time. Assuming the server doesn't change its clock for DST, midnight Standard Time would now be 1am Daylight Time.
And so I'm clear about exactly what time I'm talking about when I see the slowdown: (in case anyone else wants to see if they're having the same repeatable slowdown)
1 am Eastern Daylight Time = Midnight Eastern Standard Time = 5 am GMT = 10 pm Pacific Daylight Time