Thanks for the suggestion! One thing I've noticed is that, idly, when I've got FFXIV running my CPU is about 20 - 30 % Usage but when this 'lag' occurs it spikes up to 40 - 70 % then drops back down when it subsides. - This was at the character select screen

While in game & running around my CPU usage goes around 50 - 60% but again when this lag occurs it shoots up to 70 - 98% then drops back down again.

As for the memory there isn't anything significant that is 'hogging' the memory.