So, Intel mobile Coffee Lake high performance CPUs were released few days ago, some months after the desktop CPUs and the 15W low power consumption “U” variants (like I5-8250U). With Coffee Lake, Intel tries to battle AMD CPUs on the core count front (where AMD did very well), while still leaning on their CPUs’ better IPC per core.
In the mobile arena, the Skylake line introduced an improvement in performance compared to previous generation by bumping mobile I5 cores count from 2 to 4 (but losing the Hyperthreading). With Coffee Lake, the I5s evolved larger, more advanced cache, ~14% higher maximal turbo clocks and hyperthreading. The I5-8300H (no “Q” anymore) is a 4 Cores / 8 threads chip, compared to 4C/4T Skylake/Kaby Lake I5-7300HQ. Additional 2MB Intel “smart” cache compared to KL I5-HQ and I7-HQ CPUs is also a nice improvement.
Adding HT is not a big improvement as have more actual cores (like the Skylake improvement mentioned above), for those who really use Multithreading. That still should improve performance in some cases, but it depends. The hyperthreading feature, when not needed, could result in lower performance compared to have the application running on non-HT cores. Games that seriously utilize 4 core better not use the HT probably.
The core change is more pronounced with the Coffee Lake I7 and I9 CPUs. Compared to the Kaby Lake I7 CPUs, the lowest CL I7 (I7-8750H) gets 50% more cores + HT. The I7-8750H also gets higher maximal turbo clocks, but lower base clocks. This means that in some systems, TDP limitations can result in lower clocks and performance than the KL CPUs, if the application does not utilize the advantage of 50% more cores. I think it’s unlikely in the typical gaming situation, but we’ll have to wait and see how actual systems fair.
Note that the mobile CL I7 have decreased cache size compared to the I5s, having 9MB for 6C/12T configuration, vs 8MB for 4C/8T.
Wrapping it up, I think that for most cheaper gaming laptops and for most games, an I5 would actually be a better choice. SL/KL CPUs, coupled with a GTX 1050 Ti or even a GTX 1060 would be bottlenecked by the GPU rather than the CPU for high graphics 1080p/+ gaming with current typical games. Secondly, the I5s will be less hot and should be considerably less limited by TDP, resulting in high clocks, perhaps more so than the I7s.
An exception would be use case that utilize the CPU. Perhaps some kind of ML applications.