Of the ones I use, the Nirwen's Mercy archetype has the most noticeably damage hit (I don't use high-impact ones, so can't comment). You need to land your headshots, or it's going to take one more burst than you have time to do. Hawksaw-style pulse rifles are more or less fine; their fire rate can compensate for the damage drop; and the lowest-impact /highest-RoF pulses are monsters.