I have Horford at an 18.5 PER
http://www.basketball-reference.com/players/h/horfoal01.html
Nic at a 15.6 PER (both above league average)
http://www.basketball-reference.com/players/b/batumni01.html
Nic has a WS/48 of .125, with Horford having a .154. Block % are about the same (2.1 for Batum, 2.5 for Horford). Assist % are pretty much the same (12.7 for Batum, 12.1 for Horford). EFG% is pretty much the same as well, .538 for Horford, .540 for Batum. Horford obviously has more rebounds. TS% is about the same as well.
What I'm notcing is that aside from Rebounds, it's a lot of the same production. It's just that they bring something different than stats can show us. Horford brings the double team, Batum spreads the floor and can pass extremely well (albeit a bit crazy at times). It's really what our offense is really needing at the time, and as much as I love Horford and want him on this team, I'd almost want to trade Matthews instead, if we had the option. Though, if I am to be completely honest, I'd just want it to stay pat and ride with what we have. This is the best team we have for this system, IMO.