Bergerac or Périgueux?

I would rather stay in Bergerac, which offers better options for walks and visits to the old town (and which is along the banks of the Dordogne, where you can take a Gabarre boat trip). If you enjoy traditional markets, there are three times a week in different parts of the city (Wednesday, Friday, and Saturday).

See if that appeals to you.

https://www.pays-bergerac-tourisme.com/en

In case you're thirsty, Bergerac is also a renowned wine region,
full of Protected Designation of Origin wine varieties, white and red, dry and sweet.

https://www.vins-bergeracduras.fr/en/

Gabarre excursions on the Dordogne:

https://www.gabarresdebergerac.fr/en/

You'll have understood that Perigueux, although the administrative capital of the Dordogne, is not really a tourist destination.

We visited Bergerac this summer and found it delightful. I think three days there might be difficult to fill with activities, though. We didn't visit Périgueux.

I agree with all that JoLui has written. Bergerac is also on the same train line as Sarlat to Bordeaux so logistically it makes the most sense. Périgueux, while delightful, is north and a bit out of the way. Lots to do in Bergerac. Markets are on Weds and Saturday by the big catholic church (I forget the name but it's up the hill in to town from the river.) For accommodations, I'd look at https://www.gites-de-france.com/
Enjoy your visit!

Thanks again to all for their suggestion. Am inclined to follow path of least resistance as suggested by Kimberly and take the direct train route from Sarlat to Bergerac! Might even try an excursion en gabarre! All best, William