What hardware is more important with very long timelines?

Usually, DaVinci performance degrades quite fast while I edit longer (1-2hours) timelines (5 cams multicam in 4k) with some VST iZotope plugins applied and a few Cross Dissolve transitions. (No noise reduction, color grading or fusion effects, etc)
After some time, Playback (or even just moving around) becomes very laggy (restarting computer and/or Resolve fix it for some time generally)
Is there any one specific hardware that could improve the situation? (both on a Mac or PC)
For example, RAM? GPU? CPU?
Thanks

I've never found Resolve's performance to diminish with the duration of the timeline (I have a couple that are over 7 hours), only with what's in that timeline. (Things like effects, Fusion stuff, etc.)

What's your current hardware and OS? What driver version for the GPU?

I don't think anyone knows the answer to your question, beyond the obvious suggestion to beef up the GPU and CPU, from whatever you have (you haven't said) and hope for the best.

Notwithstanding Jim's claim above, most users break down timelines into more manageable working sizes. Note also, izotope plugins are not qualified for Resolve. They're likely to be a source of artifacts and sync error, if not playback lag.