I've found that performance differs wildly between the various campaigns/mods/standalones and between all the various FSO builds. The retail FS2 campaign is relatively pretty light on ship models and weapon effects in each given mission and consequently isn't that demanding on hardware even with newer builds. But the newer builds are significantly more demanding on the hardware either way.
For example I have an old laptop, an Intel pentium M 735 with a radeon 9700 mobility, and 1gb of ram. It can run FS2 and old Wings of Dawn with the 3.6.12 builds, albeit not with buttersmooth framerates, but newer builds will simply not start up at all. The videocard just doesn't support any of the opengl that is required.
My next laptop, a i7-2670QM with a GT 555M videocard and 8gb of ram can run the newest builds, but the framerate will be absolutely dreadful in most missions unless I turn off both shadows and deferred lighting. With those disabled, it'll run the more average missions around 60fps. But for particular demanding missions, like for example, Her Finest Hour in BP's act 3, or the final missions in WoD's upcoming episode 2 release, the framerate will drop to the 10-15ish range.
My desktop meanwhile is still an i7-2600k but it has gone through a whole slew of different videocards, starting off with a GTX 570 and currently on a 1070ti. With a GTX 960 the game would chug on quite a few occasions with shadows and deferred lighting enabled. Heavier scenes would frequently pull it down to the 30ish fps range. Putting the 1070ti in made a massive improvement, and the bottleneck on certain things would more frequently be the CPU than the GPU.
So yeah, you do kind of need a modern system for that 60fps @ 1080p with shadows, deferred lighting and all the bells and whistles enabled.
But if your pc is a bit more modest or a case of "I was high end back in 2011" you can still get some very good framerates, if you disable some of the more demanding graphical options. And even then your mileage will vary between campaigns, Blue planet will put your system to more of a test than Derelict will etc.