XF 1.2 Running out of memory on posting

We are facing an issue where we use more than 256 MB of memory just for a user to post, this seems a bit excessive so it might be a misconfiguration somewhere.

The thread being posted to currently has 27,610 posts and 239,994 views. Total daily posts in forum ranges from 30,000 to 60,000.

I have temporarily fixed this by increasing allowed memory but I fear this is just delaying the issue through brute force.

The memory being exhausted happens in different files, but always on an /add-reply URL.

We are using the following mods which, with the exception of Tapatalk, really shouldn't be touching the code when replying.

Set Rememer Me Cookie Time 1.0.1
Tapatalk 2.1.0
[bd] Widget Framework 2.4.3
[Karll] Unwatch all 1.1.0
[OnePlus] Latest Threads 1.0.0
[OnePlus] OpenID 1.0.0
[OnePlus] Widget Categories 1.0.0
ErrorException: Fatal Error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 72 bytes) - library/XenForo/Model/User.php:2422

Stack Trace

#0 [internal function]: XenForo_Application::handleFatalError()
#1 {main}

array(3) {
  ["url"] => string(70) "http://forums.oneplus.net/threads/the-storm-of-invites.36887/add-reply"
  ["_GET"] => array(1) {
  ["/threads/the-storm-of-invites_36887/add-reply"] => string(0) ""
  ["_POST"] => array(9) {
  ["message_html"] => string(128) "********"
  ["_xfRelativeResolver"] => string(61) "http://forums.oneplus.net/threads/the-storm-of-invites.36887/"
  ["attachment_hash"] => string(32) "84f246c10dbceb867507f0096ce87684"
  ["last_date"] => string(10) "1403018408"
  ["last_known_date"] => string(10) "1403167337"
  ["_xfToken"] => string(8) "********"
  ["_xfRequestUri"] => string(36) "/threads/the-storm-of-invites.36887/"
  ["_xfNoRedirect"] => string(1) "1"
  ["_xfResponseType"] => string(4) "json"
I'm thinking it could be the sending of alerts & subscription emails. Don't quote me on that though...
Decided to quote you just because that's actually a very real possibility, we send a huge amount of emails to people who watch threads. Will definitely explore that option.