It looks like all the 7.67 beta's are a slightly slower at joining all the channels. Entering "/scon -a disconnect" is also slower. This is not noticeable unless you on a large amount of networks and channels.

Stock mIRC, only settings I've changed are in the script and disabled all logging.

Video of 7.67 (left) and 7.76.5285 (right) both being opened at the same time with the same script below.

Batch file:
start C:\speed\release\mirc-7.67.exe
start C:\speed\beta\mirc-7.67.5285.exe


raw 376:*:{
  var %x 5
  while (%x) {
    join -n $chr(35) $+ $rand(10000,99999)
    dec %x
on *:start:{
  window -iez @test
  set %time $ctime

  ; Don't spam screen on disconnect.
  tips off

  ; I don't use this.
  switchbar off

  var %server_address
  server %server_address  -i KindOne $+ $beta
  var %x 20 | while (%x) { server -m %server_address -i KindOne $+ %x $+ $beta | dec %x }

on *:join:#:{
  if ($nick == $me) { echo @test $calc($ctime - %time) seconds to join }

; Test how long it takes to disconnect from everything at once.
; //var %x $ctime | scon -a disconnect | echo -ag $calc($ctime - %x) seconds

I used sol #msl (mIRC Scripting Language)