From this site.
He ran 1,000 season simulations each with Diamond Mind, PECOTA, and ZiPS projections. The average number of wins for the Reds for each simulation: 73, 74, and 69, for an overall average of 72.
Good news: He noted, however, that these simulations were run before the Arroyo-Pena trade. He said he did a run of 100 sims post-trade, and in those, the Reds gave up ~25 fewer runs, but scored ~10 fewer. That was based on Pena getting ~400 PA's per season.
From that, it sounds like a net gain of about 1.5 wins this season. So, even if the trade comes back to bite the Reds in the butt in the future, at least in the short-term it looks like it's fine.
BTW, the sims forecast the Reds to make the playoffs 1% of the time.