Upgrade advice for 4K drone footage editing please

I'm struggling editing (specifically smooth playback) mostly DJI (drone) and GH4 footage at 4K with premiere pro.

My current spec is:-

Win 10 X64

Asus X99-AII

core i7-6800K

2X16GB DDR4 Vengeance LPX 2666MHz Memory

1XRTX 2070

booting from M.2

with a string of SSD and conventional SATA3, non-RAID to the tune of about 25TB

I've considered moving to i9 but I think for the outlay, the improvement will only be marginal for premiere and my workload (OK I know render will be faster but edit is my problem, I can live with my render times already). So I'm looking at getting the most out of my current setup for another year or two.

My question is, should I go to 64 or 128 GB of RAM, even though I'm only seeing typically 60% or so memory utilisation, will increasing capacity do anything in this scenario?

If so, should I add 6 more 16GB DDR4 2666MHz sticks, or actually will going to 3333Mhz (the MoBo max) give more benefit, even with potentailly lower total amounts, so even replacing my current 2x16GB 2666MHz with 3333Mhz will have a greater impact than 128GB of 2666MHz for example?

I don't want to throw £1,000 at this for no benefit! should I just resign myself to using proxy?

Any thoughts?

regards

Nick