Excitatory impulse speed vs inhibitory Is there a difference in speed of impulses created by excitatory and inhibitory neurons?
There is a wide variety of inhibitory neuron classes.  See here for a review of interneurons in the hippocampus: P. Somogyi, T. Klausberger, J. Physiol. 562, 9–26 (2005)..

Different classes of interneurons have different spike durations (e.g. "fast-spiking" or FS cells, generally used as a marker of putative PV+ interneurons).  Additionally, different classes of interneurons have different post-synaptic receptors with specific temporal and other characteristics.  For example, GABA-A receptors have time constants of ~10ms, whereas GABA-B receptors have time constants of ~100ms (and yes, there are subtypes of those receptor classes).  You can see a modeling paper I wrote for exploration of a use for different receptor classes, as well as more references for further research. H. Sanders, M. Berends, G. Major, M. S. Goldman, J. E. Lisman, J. Neurosci. 33, 424–429 (2013)..