Why go P3D? Good question especially if you have an FSX system that is "finally" running pretty darn good (mine was - must admit a high-end system running at 4.8GHz.). Here's a personal testimonial of why I switched. I posted this elsewhere but thought it was relevant to your question:
Is it possible to have a "WoW" moment slowly creep up on you rather than a instant "WoW? That's what I think I am seeing here or should I say feeling here. After reading many threads at different P3D forums out there I "Prepar3D" myself (pun intended!), NOT to expect much difference between FSX and P3D. If anything, since P3D would be maybe a little bit of a let down as it would be in strictly default mode.
And at first, this is what I was sort of feeling. I had no tweaks set. Just see how it runs out-of-the-box. And I was not disappointed. Sure, if I stare at my FPS I was seeing relatively the same. And I did see a few "artifacts" popping up when I was in the outside Spot view. So I was telling myself "maybe I should have waited until v2.0 to try this thing". There are a few items I am not "gaw-gaw" about like no start-up screen to set up your initial flight, ATC window is not transparent, but I continued.
Have really no clue what to do for tweaks, what I did was take my FSX.cfg file, renamed it to Prepar3D.cfg and dropped it into the proper P3D folder not knowing what to expect... well actually I was expecting a crash. And I don't think Nvidia Inspector is set up right as I have made no profile for P3D - I don't think it will work if set to FSX? So I just restarted and I all I got was an "initial flight not available" warning and it went to the default flight. And it looked REALLY good. I mean REAL GOOD.
So I took off from Norfolk, the default airport. It flew REALLY smooth. This I did notice right off. Looking down below scenery just seemed to flow past me with no micro stutters. People mention better color, sharper images - that has not really caught my eye. I mean it does look clean and crisp but in my view so does FSX in my setup. So maybe this is more subjective or due to my displays. Are they using the same building textures for autogen? They seemed different - better.
Ok, big test time. Loaded up my Nvidia Surround which consists of three 27" Asus displays and a 4th 12" LCD off a second system for external gauges. This is where the WoW kept getting bigger. In FSX, with no add-ons, I moved all my sliders down to 50% (autogen Normal), traffic at 10%, weather, 60 miles - light clouds, textures are 1024x1024. At that, I was seeing roughly mid-teens (15-16 FPS). Very close to my cutoff point which is acceptable (around 13FPS and only for brief periods of time). This was at Seattle KSEA.
Now with P3D in Surround, Settings to my normal 75-80% (autogen dense), traffic 30%, weather 90 miles - light clouds, detail radius now at 6.5 miles, textures at 2048x2048 I was consistently getting mid to high 20's and at many times I am getting 30FPS (Have my FPS locked at 30). This is with three freakin' screens! I thought I would only be able to use Surround once in a blue moon like remote VFR flights. But this is something I could fly with everyday. Is Lockheed Martin doing something already with multiple GPUs? It sure seems like it. And when I do go single display mode 30FPS is most common.
I also like how they have Wide-View Aspect in the setup menu as I can switch back and forth without having to edit my cfg file like in FSX. This sets up the view setting just right when you are flying in a wrap-around environment.
So very unscientific, very subjective but I can easily say I got a very good impression with my first experience with this platform. Does it have some issues... do we miss things we have in FSX... Yes, but as others pointed out to me, this takes a back seat when what you really are seeking is performance. And that's what finally sold me. I still have FSX loaded and it will remain as I have the space and will reference it. But I can say whole-heartedly that P3D is now my main sim of choice. For me, P3D is FSNext
hope that helps somebody who is on the fence about moving forward.
Clutch