What do you consider an “improvement”? I think you can be content with your current Core, unless it’s struggling to stream your content.
If it was me and i decided to upgrade, i’d always go “newer generation” before “bigger cpu”. They are plenty more powerful and quieter and also consume less power.
Tell us the sixe of your lib and your typical use case perhaps?
(playback to x number of zones simultaneously, DSP usage etc)
Unless your current ROCK stutters or doing weird things, don’t upgrade because it will not improve sound quality. Spend your money on things that relate to the improvement of SQ like DAC, cables, usb noise filters or even speakers (probably).
There was little difference in Intel Processor architecture from Gen 5 to Gen 8 used in NUCs - just look at the single thread performance on PassMark. The chassis and cooling available didn’t allow the higher clock speeds required to wring the performance out.
What was changed was more GPU for 4K displays (not required for ROCK), on-board WiFi (not required for ROCK), on-board Bluetooth (not required for ROCK). Until you get to a NUC10 and a Turbo Boost is added into NUCs, allowing the clock speed to be dynamically increased during high load.
ROCK is an embedded application that runs headless, wired Ethernet only, and using a stripped down Linux OS.
This is when I benchmarked a NUC5i3 running ROCK it was able to do everything a NUC7i7 was able to do, and at virtually the same processor level, shown in Roon.
This including DSP using a Convolution filter on multiple zones simultaneously, while upsampling to DSD128, upsampling to 2x PCM, upsampling to max PCM, and downsampling DXD to 24/192 on the same zones. This is a 2015 NUC i3 with 8GB RAM and a 240GB m.SATA SSD. The only thing different is that the i7 would of been kicking more heat out, requiring the fan to run!
So nothing to be gained by an upgrade, and most of the folks who bought i5/i7 based NUCs to run ROCK, have probably wasted their money.