It seems to me that the RSPduo, used normally with just one front end, loads the PC system significantly less than I experienced with the RSP2pro. Never the less here is my experience.
For what it's worth, it looks like an architectural change to the software has resulted in that. Though operation with an older RSP is not recommended, I've observed that using SDRUno 1.23 with such an older device reduces the load on the system quite markedly.
I'm sure a number of folks with marginally powerful computers will be happy when 1.24 comes out.