So in the end I did walk the Tabara short cut. I gained a day and saved some mileage, and this meant I was able to shorten some longer/trickier stages around A Gudina - Campobecerros - Albergueria - Laza.
I walked it on a Sunday, so the traffic may not have been as great as a weekday. I left about 0700 in the dark and walked the first 5/6km on the Camino up to the large road junction, where I then joined the N-631 to Tabara. The first few kms on the road are a bit narrow, and there are some tight bends before crossing a high and narrow road bridge over the Embalse de Ricobayo. Lovely views of the resevoir and the colour of the stone banks, now revealed by the very low water level, was spectacular. There looked to be a roman bridge that would be submerged when the water is up. The high and narrow bridge would be interesting if there were some larger vehicles around.
The road and bends in this place reminded me of the road walk out of Aldeanueva up to Banos earlier on the VdLP.
From here the road was wider with plenty of visibility and, for the most part, completely straight. There is a very slight descent and climb around a valley and over that train line with no tracks that we kep crossing.
If road walking is not your thing, this 27km would be a real trial. It is, believe me, unrelieved road walking, with only a few places to walk adjacent to the road on the dirt.
I wore a hi-vis vest and carried a bicycle light clipped to my pack strap. I used the light early in the day and any times visibility was limited on the camino (rain and smoke from the October fire fires!) This day turned out fine and sunny so visibility was very good.
I walked the whole way relying on provisions I was carrying. Two great guys from Wexford walked an hour or so behind me. They had breakfast in Montamarta, a second cafe con leche after 8km at a restaurant immediately after the bridge over the embalse, and then lunch and beer at Pozuela de Tabara after 20km, before the final straight run to Tabara. I was unlucky, because the restaurant was closed when I went past it, and Pozuela was very dead on a late Sunday morning when I walked through. By 1330 Pozuela was open for business and the Wexford duo reported the bar there was loud and busy and one of the best they had seen since Seville. They were in great shape when they arrived in Tabara.
I left 0700, walking slowly in the dark, and arrived in Tabara at 1300 as the church bells were ringing for Sunday Mass.
In rain or other low light conditions things might be a bit different for the pilgrim. There would be more traffic on a weekday, but I must say I found all motorists very considerate. And you do miss the lovely scenery and ruined monastary others have talked about above.
Montamarta was reasonably full the night before and there was a bit of pilgrim talk about the short cut to Tabara. As far as I know, only we three walked the shortcut.