I'm running 3.1, sliders full right for the most part. Also running Aivlasoft EFB and ASNext live weather with cloud saturation at full right also. Machine specs are in my signature.
What I find is that from flight to flight, even using saved scenarios my performance will vary substantially depending on variables, especially weather. For short VFR, low and slow hops I can max out sliders, shadows and all of the eye candy with no problems. Maintain an average of 30 FPS, but to be honest it's an average. On the ground at a high demand location, FPS can bounce wildly as the view direction is calling various levels of texture loads. Once in the air, FPS will climb to the 50 FPS range and stay there until I come into the "cone" of a destination, which will most probably be another high demand draw. Like I said....averages out to around 30 FPS.
I don't run my ORBX scenery as much as I used to, but let's use NorCal as an example. There are many options offered in the scenery that you may or may not be able to handle, but the load menu will give you the options to disable the higher demand stuff that may be hurting performance. I can run either NorCal or my own HD Photoreal and see, honestly about the same performance on average, but day to day this will be more favorable to one or the other. I just adjust on the fly.
As rule of thumb, I disable tree shadows for all flights that will reach 10K AGL. No need to crunch shadows when you are above the clouds. Turn off building shadows too...at FL18 and above you don't need them.
Clouds, that's another factor. You can tweak your sim settings to adjust the clouds which will draw a lot of memory, especially if you use shadows.
Adjust your cloud shadows to a lower distance setting, no need to draw shadows that are out of your cockpit view.
I usually fly at 4096 resolution, but if I'm flying in a heavy hitter I'll go down to 2048.
Overall, I have quit comparing P3D to FSX. The changes are so significant that there is no real barometer any longer where by one can put the two side by side. I just take P3D for what it is, a work in progress. While we are in 32 bit, hoping for silky smooth, double throw down, WFO, pedal to the medal performance is not really in the realm of realistically being achievable.
One thing for sure, I'm going to start dropping all of my pocket change into a bucket and aim for a EVGA GeForce GTX TITAN X. Once LM works out the P3D VAS issues (think 64 bit), a monster card will be the game changer.
IMHO