Performance uplift will be around 10-20% depending on the game and settings used. The 6800H system won't be any faster in real terms CPU wise whilst the 12700H will be quicker in titles which hammer say a single CPU core / low amount of threads (vs the 6800H).
For context I am basing this on the following that I have tested across a number of games at both 1400p and 3440x1440:
Zephyrus G15 with 100-120w 3080 (roughly max TGP 3070 tier performance) & 6800HS
Legion 7 with 150-165w (max TGP) 3080 & 5800H
Flow Z13 with 150-165w (max TGP) 3080 & 12900H
The latter two will be faster in full GPU bound scenarios than a 3070Ti and the delta from the G15 to them is in the region of 15-25%, again depending on game and settings used.
Right now I would hold off changing over to the 3070Ti laptop from what you have as the performance jump isn't enough for the potential outlay. Annoyingly you really need a 4080 or 4090 based laptop to see any form of material uplift (for context with overclocking (~1950/15500) I can get my Legion within 10% of a 4080 based Legion at 1440p in CP2077). Downside of course is that those laptops (sans the Strix 16 with 13650HX & Gigabyte 17H with 13700H) are all £2.8k+ to buy.