Well, the thing is, if you have a 7540 with a 9880H+ or a 7550 with a 10875H+ or a 7560 with a 11800H+, you are getting pretty much the same CPU performance. However with 12th gen the difference in performance is HUGE, I have a 12600K in my desktop, with E-core disabled it's faster than the 11900K while having two core less, now if you had the benefit of the E-core, you are well above an overclocked 10900K (which is a "real" 10 core) in term of raw CPU performance. The IPC gain betwen "Skylake++++++++++++++++++++" and 12th gen is about 30 to 40% on the P-core alone...
The current chassis started with the 7x50 series, so already two generation in total... I hope the chassis will not change, that way we could still upgrade GPU of older laptop to newer GPU 😉