As has been said above, the choice between the two lenses depends a lot on what you shoot and the lighting you shoot it in. Both lenses have gotten great reviews, so neither should disappoint you in terms of IQ. But I am a bit confused as you are buying, or wanting to buy Z lenses when you have no Z body. If you are waiting and saving for a Z9 or what you believe will be a Z8, then you might be sitting on these lenses for some time. And, I assume that you are aware that F series TC's will only work with select F series lenses.
If I was in your shoes, I would decide if I still want to continue shooting with a DSLR when you get a Z body, figure out which F series lenses you want to use with either system and which are compatible with select teleconverters, and then start to plan what Z lenses you want to buy. Your 500PF will go nicely with a new Z body, albeit it is a f/5.6 lens. Your AF-P 70-300 should also be a good carryover, and it generally performs above its price point if you have the FX version. Finally, what full focal range do you need in the Z series. Personally, I would go directly to a Z body and possibly a kit lens first. The 24-70 is a decent lens, albeit the new 24-120 is getting a lot of good press these days (but it is not a kit lens). I guess I am just not clear about what is the advantage of sitting on new glass that you cannot use?
--Ken