Help to buy a new laptop please

It will be fine for the GPU. Both of those CPUs are 8th generation quad core Intel CPUs. In order to maintain the specified 15 TDP, Intel had to lower the base clock speed. When running at max clockspeed the TDP of those CPU goes up to around 25w. If the laptop has very good cooling, then it can maintain the max clock speed, or close to it.

Both 1.6GHz and 1.8GHz base clockspeeds are rather low compared to the 2.5GHZ base clockspeed of a dual core i5-7200u. The difference between 1.6GHz and 1.8GHz is relatively small so I would not bother with the i7 version of the laptop unless it is at most $100 more and I would have to think about it.

I recommend you purchase a laptop cooling to help reduce internal temperatures so that the laptop can more likely maintain Turbo Boost when playing games. However, the effectiveness of a laptop cooler depends on how the laptop itself has been designed internally. Poor / blocked airflow means a laptop cooler will be ineffective. But you will not know that until you try it.

For example, I have a DeepCool X4 laptop cooler with 4 fans that I purchased for my Dell Latitude 3540 which has an i5-4200u and Radeon HD 8850m. Temps were not bad, but I decided to get the cooling pad anyway. The DeepCool X4 did not lower the temps of the Latitude. However, when I used the cooling pad for the newer Dell Inspiron 15 7559 with the i5-6300HQ and GTX 960m, it was able to lower internal temps by 4c or 5c.

Based on reading many review of laptop coolers, at best they can only lower temps by 7c. Keep in mind that depends on the ambient temperature as well as how the internals of the laptop has been designed. The warmer the ambient temperature, the less effective a laptop cooler will be.