I spent a little time last night testing and had no issues. I did watch one tutorial which allowed me to tweak one or two minor things, though nothing I think that would benefit the problem in question (unrelated adjustments). I'll keep testing and post back every now and then. Cheers for taking a look.
Interestingly, but probably nothing related to the issue, last night while on the desktop, the graphics card fans started to spin up quite fast/rising temps, then a short while later it returned to normal. It's happened before but it's a pretty rare occurrence. Maybe time is starting to take its toll due to it being worked fairly hard for well over three years now.