Frankly, I don't understand it, because most of the users have quick responses and server is not slow.
The only explanation may be in your numbers? You've got much more messages, replies to your messages, notifications, etc. Try to clean up your notifications, pms etc.?
I missed the second bit, Whilst I have a huge amount of replies to posts, 547 pages of notifications, etc. So why isn't this happening to Tech who must surely have even more.
I'm not sure how the notifications works as they are disabled, but obviously in a selection of the new posts in a topic (when I click on the new button it would query the posts that I have replied in), but again this just confuses me even more. In theory that would be the same 'all' of the time and not in fits and starts as it currently is with some taking hundredths of a second and others taking hundreds of seconds.
Obviously with 547 pages of notification that is out of the question to manually clean-up them as the page only displays 15 entries at a time wit no way of selecting all only all on that page. I got tired of this after manually deleting 20 pages with only 527 more to go.
Is there any way that you as the Administrator can do a clean-up by date and kill all where the notification is older than three months ?
My PMs is very clear 9 in the inbox (reference PMs) and 9 in the outbox.