I have the i7-6700k Skylake CPU from Intel. It is the fastest 6th gen processor out of Intel's 6th gen line up. And the best processor I've ever had on a PC. The i7-7700k is pretty much the same just a slightly overclocked clock speed.
However Intel does sell some 8 core 16 thread i7 CPU's which can do 4-5Ghz. My laptop has an i5-6200U processor. But I've been amazed at how well my i7 processor can do.
For this game, it pays to have an i7 quad core processor (4 cores 8 threads) minimum, with above 3.4Ghz clock speed. Especially if you want to play larger parks on 1920x1080 Ultra preset full screen.
I have a sandbox map with moderate scenery, 22 rides, 6k population, playing in 1080p Ultra settings (full screen, not windowed) and manage 24-40fps. I also have an EVGA GTX 1070 SC, which is better than a regular Gigabyte GTX 1070, since mine has a GPU clock speed of 1888Mhz, that's even faster than the GTX 1080 standard version from Gigabyte (but it has less cores and possibly vRAM than the 1080. However the GTX 1080 is just far too expensive). The GTX 1070 is already overkill on many games including The Sims 4.
However no matter how good your hardware, if you add too much detail, you are going to run into lag. That's a fact. Big Youtubers have mentioned it.
The i7 6700k and 7700k are reasonable priced. $200-$450 at worst. But it will do a better job than an i5, due to more cache, and a faster clock speed. The i7 processor line up represents like the best of what Intel has to offer.