Hello.

I am considering an upgrade of my i5-8400 in my Dell XPS 8930.

For primarily flight simming, can you please advise on whether an i7-8700k or i5-9600k would be the better upgrade?

The i5-9600k is literally half the price.

Thank you in advance,

Glenn

I recently upgraded to the I5-9600k and am quite pleased.  It is common knowledge P3D does not make good use of hyper-threading.  The real question out there is the requirements of the upcoming Microsoft MSFS product.  As most games rely primarily on single core performance, the hyper-threading issue may still exist.  Waiting may be a good option.

In any case, I am a happy flyer and would expect decent performance with MSFS 2020.  I don't need to be the best performer but just comfortable.  If I can have good looking scenery, excellent weather depiction and nice flight dynamics without stutters in a nice aircraft like a PMDG, then life is good.

Of the two chips you've listed, the 8700k is the better chip since it's more versatile having HyperThreading enabled out of the box.  Sure you can save some money with an i5, that's why they exist.  If you want the best performance though, you'll want to go with an i7 or even an i9.  Since you likely can't overclock, and flight simulators LOVE clockspeed, you're going to want to buy the chip with the highest clockspeed out of the box.  Right now, that's the i9 9900ks, though I am unable to confirm whether your motherboard has support for this specific chip at this point in time.  I can however confirm that the 9900k is supported, and that would be the next fastest chip.  

For the price of the 9600k right now its a great chip for P3D. Go for it!