Well thank you for your incredible insight into this subject. Clearly the reason I'm having woes with one specific map, the same woes had prior to the optimisation of the other maps (which for the most part is now resolved), is because my computer isn't up to spec. The reality that the game isn't even utilising all my RAM is of course a mere technicality and the GTX 970 is just unsuitable to play this one specific map. Gotcha.
I'll go buy a new PC so I can play this map throughout next week without lag, waiting for it to be optimised to run on reasonable hardware would be unreasonable.