The recipe for this was:

3 cups plain flour

1.66 cups waster

1.5 tsp salt

0.25 tsp yeast (left hand loaf) vs 1 tsp yeast (right hand loaf)

1. The high-yeast loaf rose more and more quickly

2. Things evened out in proofing, which initially reduced them both to the same size

3. The high-yeast loaf spread further: this was exacerbated by proofing for an extra hour while the first loaf baked. I had expected the yeast to be “exhausted” but in fact it was still bubbling

4. In terms of results: taste was identical, crumb was identical, oven spring and shape were better in the low-yeast loaf, probably due to the high-yeast one spreading

CONCLUSION: add more yeast for a quicker rise, particularly if you plan an “instant” (no proofing) bake