I've put a Xeon E3-1265v2, which was already quite the upgrade over the dual core Xeon it came with. And then added another 8GB of RAM for total of 16GB. I have 2x1TB SSDs as my cache drive pool and 3x14TB HDD as my array (1 parity). Running Unraid as the OS. I installed the official Nextcloud docker first and had the app files on the SSD as recommended by you as well as the template itself. I also attempted the official AIO docker which includes everything including "High performance backend for Nextcloud, Talk and TURN-server". I opted out of Office, Talk, and ClamAV on the AIO install as well as disabling apps within NC that I won't use like their garbage photos app and Deck, for example. There are a few others I just won't use. And it still runs poorly. Perhaps we have different opinions regarding acceptable wait times for certain tasks. But I can say even just testing it with very few items synchronized, there have been several conflicts within Tasks and Notes. I'm talking a half dozen notes and tasks colliding with one another when syncing and throwing errors.

Please understand I mean no one any ill will nor am I trying to disparage Nextcloud as a solution (other than the photos app, lol). And I thought I made it clear that I understood it to be a limitation of my hardware, not the app itself. That said I've noticed people get weirdly defensive of Nextcloud anytime someone has any complaints about it. Not just here, but on any forum I've searched for solutions or options to help with performance. As if they're personally invested in the company or something. If it works for those folks, more power to you and I wish you many happy years of service with the app and many 1s and 0s flying back and forth with speed and accuracy. It's just way more app than I need to run.

These tips are all solid, and reflect my setup. Database (MariaDB) and PHP files on the SSD, data storage on spinny bois. Don't underestimate the importance of a recent enough version of PHP, OpCache, enabled, and so on.

There's a whole chapter on performance tuning in the manual, and the "Security & setup warnings" part of the administration settings should point out some configuration issues, when it finds them.

My setup might actually take a (smallish) performance hit because I use btrfs for all my filesystems. Just don't get roped into the whole "wsl on Windows" thing, that's just not going to work out, it's a kludge that MS offers to not bleed users to Linux too much, but it's certainly not meant for server workloads.

The hardware should not be the bottleneck at all, the 1265 in OPs machine should not be significantly slower than the 1280 in mine.