^^ I don't recall any warp speed phaser battles between ships of different warp velocities in other series except for TOS. "Journey to Babel" had a Orion ship phaser strafe the Enterprise at a much, much higher warp difference between the two ships.
Also, "The Ultimate Computer" seemed to imply that the Enterprise fired phasers at different ships while accelerating between different warp speeds.
So, in TOS, different warp speeds don't seem to matter. TNG, etc, I dunno.