It is necessary to take in consideration many variables in order to get a good performance notebook. We need to check the type of memories and qty of GBs, type of drive (mechanical or Solid State Drive) and type of processor (number of Cores, speed, embedded graphics) and dedicated graphics card (optional).
I suggest you to make a list of your daily tasks, this information will help you to determine which system is going to fulfill your requirements. If you play, edit videos or Audio a dedicated graphics card is recommended.
I7 processors have more Intel® Smart Cache memory, usually more speed, there are versions with 2 and 4 Cores.
Now, the newest 6gen Core™ processors support the fastest memories DDR4 2133MHz at 1.25V vs DDR3 1600MHz at 1.35v (5th & 4th gen). They have embedded graphics Intel® HD Graphics 520 / 530 or Iris™ 540 / 550.
In the case of 6th gen i5 processors, there is only 1 processor with 4 Cores. Additionally, 6th gen processors save more energy than older versions.
Below links give the available mobile i7 4th processors and i5 6th processors.