You are asking a lot of different things in one question. I would try to answer em all. Pardon if I miss anything.
First things first, there are very few games right now supporting Real Time Ray Tracing so if you will get the laptop with RTX GPU right now you won't see any improvements in gameplay. It's good for future proofing, but still it's going to take time for game developers to completely embrace this new technology.
Side note - There are huge discounts on laptops with GTX 1070 and 1080 right now.
Choosing between RTX 2060 and RTX 2070
RTX 2060 is a great mid-range GPU. It outputs similar performance as the GTX 1070 so it should be great for 1080p gaming at high graphics settings.
RTX 2070 is great for professional level gaming. It will output better performance than the GTX 1080. 2070 Max-Q will be slightly slower though, but it should be great for playing some of the most demanding titles at high graphics settings.
Performance gap is definitely significant, but whether you should spend extra and get the RTX 2070 depends upon your requirements which you didn't mention.
1660 Ti looks promising from rumors and leaks though. But, nothing is confirmed yet so.
Non IPS vs IPS
IPS are great for content creation and color-accuracy works. They also have better viewing angles. So, if that's something you have to deal with then get the IPS.