If your nMP is the 12 cores + dual D700. I won't be surprised that the nMP is faster than your cMP.
The nMP has better CPU performance on both single thread and multi thread operation (even though not much). And that's just the raw power, the nMP has newer and better architecture. It's highly likely that it can finish the same job faster.
Dual 390X should be significantly stronger than dual D700. However, very likely FCPX is so optimised for the D700. Therefore, D700 can perform better actually on most simple task. And unless you really doing something that beyond the D700 can handle, the 390X may not able to show off it's power.
For photoshop, it's mainly CPU single thread, RAM size + speed, and hard drive speed limiting. And nMP sure has better CPU single core performance. As long as the RAM size is reasonable, the nMP's RAM should also performance better than the cMP. For SSD, the nMP SSD sure is fast enough to handle photoshop, so no big difference between cMP and nMP.
So, unless you are doing something that clearly favour the cMP. e.g. a software that can utilise CUDA. Or something that can benefit from >5000MB/s read / write speed. Or utilise the 10Gb network. etc. For most simple task, the nMP should work better.
In fact, the nMP is a FCPX orientated machine. I will be very surprised if a maxed out nMP still slower than the cMP in FCPX. So far, AFAIK, the fastest Mac (real Mac) in BruceX test still the nMP.
I rarely heard that the cMP can finish some normal real world jobs that significantly faster than the nMP (basically except the software that optimised for Nvidia GPU). The advantage of the cMP is that we can build a machine that comparable to the nMP with just 1/3 of it's cost. Or we can config / upgrade the cMP to make it more fit (or cost effective) for our work.