A few weeks ago, i read here that someone else uses an Optiplex. Maybe this is usefull for him/her.
In my studio, the main workload lies on an aged Dell Optiplex790 with some I3 Core2Duo (2cores), 12GB RAM and an RME Hammerfall HDSP 9652. The machine mainly runs Ardour and Hydrogen under Jack (5,3mSec, 1024 ports). It worked very well over the last years, but for about 4 months or so, i got a lot of xruns and the system reacted very delayed. My first impress was, Manjaro was the origin of the problems. I tried different distribution kernels, Liquorix-Kernel, a self-build kernel, nothing helped. A look on htop showed me cpu load of 100% on actions. I switched then back to slackware with a self-built realtime kernel, which worked for a few weeks. Some updates later, xruns started again and the load was again at 100%, even under 10mSec (fortunately, at that time i did recordings not on that machine - for mixing, the latency doesn't count for me, as long as there are no MTCs involved). So in the end: the machine is way to slow, because i also track on this machine directly, and not everyone is willing or able to work with 10msec or more of latency. Two years or so ago, i had allready thought about a cpu-upgrade. The fastest one the board is able to drive is an i7-2600 (4 cores). It costed then something around 60/70€. Now it's more than 200€. For about 500€ i could get a brand new machine (need PCI for the HDSP). I decided no give a used cpu a try for about 30€. This works great!
You have to prepare the board: you need the freshest BIOS (at time of writing this: vers. A22) to use this cpu. I updgraded from A13, that was a bit tricky: you need a DOS-System to upgrade, and the currently available FreeDOS1.3 loads some drivers, that make it impossible to upgrade. So, when it boots, you have to press F8 and answer all upcomming questions with "n", then the upgrade of bios works. Keep in mind, that you might have a different keyboardlayout, than an en-layout, when answering the questions.
The change of the cpu itself is very easy: you need a Phillips screwdriver to umount the cooler with the cpu-fan ensemble, that's all. Of course, you need some thermally conductive paste between cooler an cpu. The hardware stuff is done in 15 minutes, if you take the time to blow out the dust of years. Connecting 6 lightpipes to the hdsp card took more than 20 minutes. The engineers, who designed this connection, should be punished somehow...
Now the machine runs on 4 cores (are this 8 threads in htop?) with a load of 30% per cpu, peaking to 35% (htop) and a latency of 5.3mSec. Ardour stays under 55% cpu load. With my thickest session, on my first test there were no more xruns, even not at the start of a transport. For fun i will try 2mSec this evening.
The powersupply works great, and the cpu doesn't seem to run hot. But i had no time to work heavily on the machine, this will happen this evening or tomorrow. Maybe, if someone is interessted, i will have a look around 20 o'clock UTC into the jitsy round.
