dragbike

With REX and ASN you may want to try a CPU affinity mask that leaves one core free. Other than that, you can check your GPU usage when the CPU is not fully utilised. MSI afterburner (amongst others) will help you with that. If your GPU is flat out then your CPU will wait.

Prop pitch will have very little effect taxying. Try a dab of brake every now and then to regulate taxi speed. Use fully fine for takeoff and pull back the lever to set the RPM you want in the cruise, then set the power (throttle) to what you want. Ignore the engine sounds from the sim, as they vary with throttle opening, not actual RPM! Remember prop fully-fine for finals.

An SSD will improve your loading times significantly. When you add new scenery you will not need to re-optimise your HDD to get the best access times. Reading scenery from an SSD will reduce any tendency for stuttering. The faster access times of SSD will either reduce blurries or allow you to reduce the Fiber_frame_time_fraction; this can further reduce the potential for stuttering and may give a small FPS improvement.

To add to DylanM's reply... I have a similar system to you (i5 4670K @ 4.5 and GTX780 being the significant differences). Obviously with your i5 @ 4 you've already done some overclocking. I recently turned down my OC from 4.6 to 4.5 and aggressively ramped up the memory speed. This gave a very noticeable improvement in smoothness. I stopped trying to OC the GTX780 and was rewarded with yet more smoothness. I've tweaked Prepar3d.cfg to set AffinityMask to 15 and have also set TessellationFactor to 100. The 344.60 Nvidia driver also helped. I've found that 3rd party AI can worsen stuttering too.