It indeed reached the rest of Europe, but i dont think it had more impact than the later one. I belive the 14th century plague was on a much larger scale. I haven't yet managed to study alot on this one, but i can provide some details about the Justinianic Plague. Alot of people died. Around 35% of the population of the empire perished, this led to an economic and demographic crisis. The first wave of the plague lasted for about 4 months, the ones after that one afected the rest of europe too. The city of Rome is an example. The plague keept coming back for around 250 years. In the aftermath it led to famine. There is much more to the Justinianic Plague than what i wrote here. You can find first hand info in the writings of Procopius of Caesarea, John of Ephesus and Evagrius, all of them lived in that period.

Edit: About the lethality, the sources say that it reaches 10,000 deaths per day in Constantinople, but this can be an exageration. Also they metion people dying right after they were infected, without any simptoms, some managed to eacape the desease, an example being Justinian himself. By the description of the first wave is quite gore-ish. Corpses of animals and humans on the streets. Huge holes in the ground that could contain around 70,000 corpses. I hope this gave you an ideea about what was going on at the time.