Is this for HT or music only?
If it is for HT, I would work towards switching to one of the ID sub companies (such as SVS, Hsu, Rythmik, PSA) or Monolith or Outlaw (who smartly hire specialized designers to do their subwoofers).
As Shady says, the difference is the amount of mid-bass vs deep-bass.
For most music, I believe the R-115's will provide deep enough bass to cover things well (and complement the R-112's reasonably well),but for HT, having the extra power in the deep bass when the depth charges go off is
more fun. If money is no object, I would get the others; but if you work hard for your money, I'm not sure you will get enough improvement for the limited deep bass
of music to justify the cost!
You can try out the SVS subs for free. Verify (it has been a long time since I have visited their site),but they used to give you 45 days to determine if you liked your purchase and they would actually pay return shipping if you did not - IOW, you pay nothing to try them out, if you don't like them!
Here is a little video on the PB3000 vs dual Klipsch R-115SW's with some REW measurements. Note that these measurements are in his room (your room will change everything), but the relative differences in the measurements has at least a little relevance!: