I'll preface this by saying I'm by no means an expert having visited just one time the region. And our faocus was almost entirely the Perigord, with just a day's visit to the Lot on the drive over. Ironically, I much preferred the scenery in the Lot and I'm sure we'll get back there and spend some time just visiting that area. While I enjoyed the Perigord and the number of very fascinating places to visit is huge, I don't feel drawn back at all, but that's just me.
Anyway, since our vacation as about the same length as yours will be, I thought just sketching out our trip might help give you a sense of what's doable. We are not fans of spending lots of time driving to get to our day's destination, so we tend to go for shorter stays in a few different areas - at least we did in the Perigord and it worked out quite well.
We had three bases (4 nights in each)and I'll list sites we saw from each, to give you an idea:
1) First base Brantôme - Château Puyguilhem, St. Jean de Cole, Château Bourdelles, Aubiterre and various villages around, Périgeux, Abbey Chancélade, Prieuré de Merland,
2) Lès Eyziès - Font de Gaume, Combarelles, La Roque St. Christophe, Montignac, Château Hautfort and Château Jumilhac,
3) Sarlat - Gouffre Proumeyssac, Saint Cyprian, Limeuil, Cadouin, Beynac, Roque-Gageac, Montfort, Domme, Montpazier, Castlenau, Belvès
Hope that helps a bit.
All I can say is trying to do both the PErigord and the Lot from just one base would be way too much driving for me.
- Kevin