I cannot give you advice about Gebennensis because I do not walk on it. I met a number of people who walked on it: it seems to offer nice sceneries but is demanding and quite lonely.
However, I walk Podiensis. Some people think Le Puy-Cahors is the best part of this route, but I do not share this advice: I think there are different parts on Podienis, but all of them is worth walking it:
- Le Puy-Conques offer marvellous sceneries, among which the Aubrac, and invigorating food (saucisses-lentilles, aligot, truffade...)
- Conques-Cahors is very nice, especially if you choose the Célé Valley, as some members advice. You can even rent a canoe to go down a part of the river (for instance from Marcilhac to Cabrerets).
- Cahors-Navarrenx is not bad, even if you will see lot of corn fields. Food is also worth mentionning it: duck under all its form, armagnac or floch de Gascogne as aperitive.
- From Navarrenx to SJPP, Bearn and Pays Basque will offer you nice landscapes and friendly welcome.
Furthermore, as you wrote, doing the whole Podiensis make sense.
Anyway, do not miss the early mass in Le Puy: even if you are not a catholic, even if you do not understand a bloody word of french, this mass is made for any pilgrim, and at its end you will actually see the way, nearly until Santiago !