I recall times when Negi was excited he'd 'leak' wind magic but I was under the assumption that Dark magic is specifically fueled by negative emotions whereas Negi's normal wind magic is fueled more by just determination/ability to use magic.
Of course I could be just pulling stuff out of my butt, thats always a possibility
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As far as being prone to anger I'm not sure if the Dark magic has an effect on that or not, Negi has always been protective of his students, if you recall the incident where he first found out some of his students were being mistreated as slaves. Considering its Fate's fault his students were scattered and put in danger, and the fact Negi has been brooding on this for almost a month, asking for Asuna as a trade was probably the last straw.
Whether or not Negi becoming a dark mage makes him easier to anger though is still hard to tell from what little we've seen of him after acquiring Magica Erebea.