Haste btw does not = faster dots. The duration of SWP is the same regardless of your haste total. Haste increases the damage of your Dots by the way of additional ticks of damage (which is reflected ingame by the damage numbers on dot tooltips increasing with haste, in addition to intellect and spellpower) Its not quite as simple as 'stack haste' as a rule though because as im sure you're aware a significant amount of the gear choices that have the highest amount of secondaries you want do not have any primary stats on them, So a 'max haste' set will have significantly less burst potential then a set which is prioritizes spellpower for example, because the damage of your non dot spells does not increase with haste (although it does reduce their cast times)
To maximise your potential the ideal setup is having several gear sets and swapping between the situation your in eg 'maxhaste.set' fpr your classic eots mid fight, max int if you find yourself guarding a base or trying to kill EFC. I personally value burst damage (the value of which is not reflected in damage totals) significantly more then rot damage almost all of the time in a wargame environment, but im sure peole disagreee have different views about this.
TLDR Get all the gears and all the sets and prepare to get signifcantly more frustrated with 'combat' and why the fuck youre in it when your literally just rezzd alone at farm.
edit - Doesnt change much but its worth noting that haste not only provides additional damage to vampiric touch but also reduces the cast time, so its value for that specific spell is increased compared to instant cast dots of which I think all the others in the bracket are (I might be wrong)
Edit - I play a healer and this is potentially all incorrect