Hi, I have a Alienware X51 R3 purchased in April-2016 with only a graphics card update (upgraded GPU to Nvidia 1060 Founders Edition 6GB).

Intel(R) Core(TM) i5-6400 Processor (6MB Cache, up to 3.3GHz with Turbo Boost Technology)

8GB Dual Channel DDR4 2133MHz (4GBx2)

1TB 3.5inch Serial ATA (7,200 Rpm) Hard Drive

Windows 10 Home (64bit) English

The PC is used exclusively for  Xplane 11, Forza 7 and some other games. So far the performance has been decent. I am looking for advise to upgrade the:

CPU - to i7-6400,4 Cores, 8 Threads.  @3.4GHz Skylake (2015)

RAM- from 8Gb to 16Gb

Will these upgrades result in ~20% performance gain, are these worth it, should RAM be increased to 32Gb etc. An advise is appreciated. My budget is <$500.

Thanks in advance.