I've been using gabapentin and pregabalin semi-interchangeably for around 2 years for my ME/CFS and small fiber neuropathy. My recommendation is to start with the minimum dosage available - usually 100 mg gabapentin or 25 mg pregabalin. If you don't have a tolerance to gabapentinoids (which seems to be the case), you will likely get some benefit from this dose level. (Note that pregabalin is ~5x as strong as gabapentin by weight).
Gabapentinoids are great for pain and I find they can be somewhat helpful for more specific PEM symptoms. Pregabalin has similar effects to gabapentin, though general consensus is that pregabalin hits more quickly/reliably and is less sedating. Regardless, they can both cause sedation so some people prefer to take them at night to help them sleep. However either would likely wear off by morning especially if you use them regularly.
The problem is that regular use inevitably leads to tolerance. Not as quickly as benzos, in my experience, but if you take them for months and get good and dependent on them, reducing your dose can cause some pretty nasty withdrawal. My strategy initially was to only take them intermittently as needed, and dosing 100-200 mg gabapentin a couple days a week did not cause any tolerance to their effects. If you find that that frequency works for you, it's a pretty low-risk routine.
Ultimately, I ended up needing to increase my dose out of desperation, and at my highest I was taking 400 mg of gabapentin every day plus at least 100 mg of pregabalin (though all things considered this is still not a very large dose - a lot of people take 1800 mg of gabapentin a day, sometimes even more). At that point, keeping my 'minimum' dose did not even provide any benefit. I was able to gradually reduce my dose and now I am back to my original intermittent routine.
