Do the road works start at the A605 or before that?
After you leave Oundle on the return, you drop down through the Nene Valley and back up to the A605 (~3km). It's the whole junction with the A605 that's being reconfigured, the road works start about 150m BEFORE the junction, i.e. just before Barnwell Road drops down to the junction.
The problem is that the works extend another 400m AFTER the junction, and that is a LONG way to TT with a queue of cars on your back and the traffic facing you being given a green light in the meantime, especially after 150km, and there is nowhere to hide — the white line on the left is the limit of the road and NOT a cycle lane, and there's a line of cones all the way down the centreline.
Taking the shared-use path, you can wave at all the queuing motorists and cross in relative safety at the other end, while beating the lights anyway, as it's a four-way sequence with something like 600m passage from one end to the other on the main road, so the wait is interminable, whereas the shared use path you can just switch over and carry on.
I rarely recommend cycle-specific infrastructure over just riding on the road, but this is one of those times I think it's a Good Idea, for this year at least.