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.