The Recommended System Specs for Total War: Warhammer 2:

OS: Windows 7 / 8 (8.1)/ 10 64Bit
Processor: Intel® Core™ i5-4570 3.20GHz
Memory: 8 GB RAM
Graphics: NVIDIA GeForce GTX 770 4GB | AMD Radeon R9 290X 4GB @1080p
DirectX: Version 11
Storage: 60 GB available space

My Specs:

Mircoflex 25B
Case, In-Win C638
750W Silent Power Supply
MB, Asus Z87-A
CPU, Intel Core i5 4670
Memory, DDR 3, 8192MB (16GB)
HD, 500GB, SATA, WD 7200RPM
Samsung 24X DVDRW
EVGA GTX 1070
Windows 7 Home Premium
Asus 20 LED Flat Panal 1920 x 1080p

I guess I was asking for too much of certain games.

Total War games have always been demanding if you want to have Large Army on Large Army battles.

I mean even Medieval 2 is still demanding if you exceed the army numbers count.

You understand that an upgrade would mean new:
Processor $380 for an 8700K, $260 for an 8600K
Motherboard minimum $120
RAM $200+ and rising
and probably new Windows license too.

Lots of money for a not so big update but the two extra cores will of course make a difference in some games.

two extra cores?

Yes, the big advantage the 8700K and 8600K have over the earlier generations' top processors is that they come with six cores instead of four. A lot of games cannot use those extra cores though but there are a few slightly older than can and new ones are released regularly that certainly can use them. Sorry not going to look up that Warhammer game you mentioned but it is the type of game that might support as many cores as you can throw at it.

(forum still bugged grrr)

So I think I should aim at a 8600k i7 than.

NOOOOOOOO:)
8600k is an i5 and has 6 cores 6 threads. You want the 8700k which is i7 and has 6 cotes 12 threads

That is the one without hyper-threading. Remember that the only motherboards you can use are those that come with the Z370 chipset.

K. 8700K it is than.

Please tell me I don't have to upgrade to Windows 10 to have this work?

I don't know how it works. If your windows version is retail, I think you can transfer it.

There is some trickery needed to make the modern processors work on older Windows. All I know is there are people out there who have managed to do it but I do not know if there are penalties.

While an i7 over an i5 would help, the difference will not be massive for gaming. Games such as the Total War series would improve, but keep in mind that the majority of "AAA" titles rely heavily on the GPU,

I have 3 gaming systems: i5-2400, i5-4590, Ryzen 1700X. The i5's being 2 generations apart, perform almost the same, meanwhile the 1700X (having 16 threads) still performs similar to the i5's in gaming but lets me multi-task more efficiently.

An i5-4670 for 1080p gaming is still a very good CPU, may I ask what graphics card are you running?

OP listed system specs in post #16, so a GTX 1070.

I can imagine that kind of game being in a genre where the 8700K makes sense over the 8600K but not going to look up benchmarks for games I have no personal interest in. Of course, if you want lots of cores, you should buy AMD Ryzen instead for more cores/$ but at a bit lower clock rates.

Aren't Total War games known to be pretty poorly optimized? I don't think an upgrade from your current hardware will net much of an improvement.