I was thinking of 4k60, do you think the 3080 is capable of that or should I go for the 3090?
Almost certainly not "worth it", but the users who buy the top tier card from the off are not usually too concerned with "worth it", they just want 'the best'.
As for whether a 3080 is the card for you, really depends on your needs/use-case/budget.
I'd say that it entirely depends on what your monitor setup is going to be. If you're running just a 60 - 120Hz monitor, then forget it. If you're running like triple 240Hz 1ms monitors or you're going VR then I could see it being worth it. But yeah what GPU you get almost entirely depends on your display configuration.
I was thinking of 4k60, do you think the 3080 is capable of that or should I go for the 3090?