Well Big Camp has been and gone so time to post the results.
Overall I'm more than happy.
I clipped the nest in place before pegging out the guy lines, which meant it actually fit well. I cut a small amount off the poles which I might not have needed to do had I thought about clipping the nest in place before guying before I cut them! My pole length is now 135 cm.
The seams held up well enough against the end of the pole, no obvious stretching and no water ingress.
The nest did seem to sit very close to the fly, actually touching it in places. This did mean a small amount of water droplets formed on the nest mesh. None of it made it through the mesh and it might have been due to condensation. The amounts were so small as to dismiss them.
The wind was up but not very strong, moderate in places with strong gusts. Stronger than normal though. This was my biggest concern as it pushed the whole of one panel of the fly against the nest, but given my comments above about the amount of water ingress I don't think it was actually a problem.
The nest worked well, great to be able to sit off the ground to get changed etc. Space wasn't an issue although you do have to work out how best to pull on your trousers! Overall it was great for one, plenty of room for kit. I didn't do any cooking or spend any significant periods of time awake in it though. I'm just about 6 foot and had no problems with the length. No obvious drafts.
The cardboard vent openers did the job, just a bit bent.
It was very cold for UK and May. Friday night I slept on a 3/4 length thermarest with a 3 season bag. By Saturday I'd added a closed cell foam mat and a second bag (just because I could, we had spare kit knocking about) and had two really restful nights sleep. Woke up to frost on the outside of the tent several mornings.
Will become my first choice probably with a gortex bivvy bag instead of the nest for hill walking and field camping.
Any questions just ask!