I've been using WTFast free trial and it solved my issues. They added a new Montreal server recently as well so I'm guessing that has something to do with XIV and a sudden upsurge in people using WTFast to connect to it. After it ran out I tried the normal internet again and was hit with lag, constant error 90k's and freezing title screen, it was even making my internet connection disconnect and re connect which was very strange. Anyway after having all that crap come back after a trouble free 30 days; I decided to just pay the $5.99pm for it (£3.50 for me in the UK). As soon as I re booted through WTFast it was smooth sailing once more.

I know it sucks to have to pay extra to play something you're already paying for, but for me; a small additional payment each month is worth not having to worry about all the issues I was struggling with.