So which of the following would be best to pair with 3080 ftw3 ultra
1) The best of the Rocket lake cpus that come out next quarter
2) 5950X
3) 5900X
 
I am a long time intel user so would like to stay with them if they will be competitve.   But if they can't compete I will go AMD cpu.
Strangly I am seeing bechmarks that the 5900X outperforms the 5950X flagship cpu in games.   
Which of these 3 would be best to pair with a 3080 ftw ultra or will it not make much difference since they will all be a big step up from my 8700K.   I run 4K and 1440P, I don't do any 1080P.   

At 4K it doesn't matter so much, but at 1440P and below the new Ryzen CPUs are currently top dog for most games. Intel did say that their IPC gain is like, 15 or 20% for the upcoming CPUs... so who knows.

5900X is more logical, unless you really need the extra cores on the 5950X.  The 5900X actually performs better in some games because of the higher boost clocks.
As far as how much better it will do than your 8700K, just watch some YouTube reviews on the 5900X, it blows it out of the water in both production, and to a lesser margin, in games.
I do agree you should at least consider slightly lower tier AMD CPUs if you don't need the extra cores for production/work purposes, anything over 10 probably isn't going to net you anything useful otherwise.

If you have a 8700K your MB might support a 9900K. My 9900K runs 5 GHz locked all core with only air cooling. This puts it behind but reasonably close to the 5900x from benchmarks I’ve seen (for games). Then I would skip rocket lake and focus on alder lake which will come on the heels of rocket lake but have DDR5 PCIe 4.0 and be 10nm. I’m not sure I would swap out a MB for Zen 3 since I believe it’s the last stop for the AM4 socket. Just my opinion.

nesbit
If you have a 8700K your MB might support a 9900K. My 9900K runs 5 GHz locked all core with only air cooling. This puts it behind but reasonably close to the 5900x from benchmarks I’ve seen (for games). Then I would skip rocket lake and focus on alder lake which will come on the heels of rocket lake but have DDR5 PCIe 4.0 and be 10nm. I’m not sure I would swap out a MB for Zen 3 since I believe it’s the last stop for the AM4 socket. Just my opinion.

Rocket lake has pcie 4.0 as well.  Also I don't think I will touch adler lake as they are going the weird laptop 8 big cores 8 little cores with it.   Games have 0 need for 8 extra 1.5GHZs cores.  From what I have read about how that tech works it will not help games having 8 little slow cores taking power and creating heat that could have been used to make the big cores faster.  To me adler lake seems like a battery saving laptop cpu stuffed into gaming desktops.   I will definately either be getting one of the new AMD chips or the top Rocket lake.   Guess I am going to have to wait for the stats on rocket lake and then decide.   My 8700K will hold me over for a few months.