However, our test results also show that the performance delta between the Core i5-8250U CPU and the Core i7-8550U processor is really small so it's probably not worth paying extra for the Core i7 chip.

If you're shopping for a laptop and there's a model with 8th Gen Core available in your price range, you should definitely prioritize it. This means the main difference is that the Core i7 has more performance, can run multiple programs easily, and way faster than the 4th. You’re mostly correct though, the newer generation comes with more cores (6 cores for 8th gen i7). While the performance benefits of 8th Gen Core processors vary depending on the task, there's no doubt that it provides a huge boost, particularly on multi threaded tasks. A computer built around a 4th generation (Haswell) Intel Processor, and all its orbiting components, against a computer built around a 6th generation (Skylak. Incorrect, the core i7 4th gen comes with 4 cores and you can tell just by doing a simple google search.

4th gen vs 6th gen i7