I know that the GTX 1080 /1070 series laptops were very close in performance to their desktop counterparts. They used the same chip and were within 10% of performance of the desktop versions. That was a great step forward for gaming on laptops
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Unfortunately, the new 3 Series laptops are not close to their desktop counterparts with performance at all. That goes for the 3080 mobile and also the 3070 mobile. I'm sorry if you didn't want to hear this.
Max Q versions take a substantially worse hit in performance. All these laptops should have different names all together so that consumers are aware like "3070 Light mobile version" or "3080 Light mobile version" after all Nvidia were quick to do the naming change with "Light Hash Rate (LHR)" cards.
GeForce RTX 3070 Desktop vs RTX 3070 Laptop 115W
"When comparing the RTX 3070 Laptop GPU to its desktop counterpart, it’s a bit of a bloodbath.
At 1080p, the desktop is 35% faster on average than the 115W laptop variant, it’s undeniable that the desktop GPU is significantly faster and not really in the same performance class."
https://www.google.com/amp/s/www.techspot.com/amp/review/2206-geforce-rtx-3070-laptop-vs-desktop/
Also on laptops , cooling is a big issue and with a desktop you can use faster RAM and CPU and better cooling to even increase that 35% performance to like 50-60%. So a desktop 3070/80 PC can be made to be 2 to 3 times faster than the laptop.