You got a HUGE from me when I read that…
I stole 4GB (half) the RAM from this old d780-c2q at one stage as I needed the RAM for testing of another box, not expecting to see any difference with how I then used the box, but BOY was I wrong… (I’ve written about this before). In that case I could restore my speed via swap config.
I much prefer the old c2q-q9400 boxes even with spinning rust drives over things like thinkpad x201 (i5-m520 with HDD), vaio ultrabook (i5-9400u & SSD), or samsung 700t1c (i5-3317u & SSD) and no doubt RAM is part of why as they all only have 4GB RAM. (I do like desktop form factor, but I could connect an old IBM Model M keyboard up to a laptop too)
CPU plays a large part too; I recall one box where Lubuntu significantly outperformed Debian in live QA testing, but that box had a different (lower-end) CPU to other boxes I used… I recall noting how MATE (Ubuntu-MATE) slowed down rather markedly on some CPUs as it ported from GTK2 to GTK3, yet on other later CPUs I couldn’t see any difference. My old c2q’s were not sold as low-end products.