Three isoperimetric results are treated. (i) At a given pressure gradient, for all channels with given (cross-sectional) area that which maximises the steady flow Q steady has a circular cross-section. (ii) Consider flows starting from prescribed initial conditions developing from a prescribed imposed pressure gradient, either periodic or steady. For such flows, amongst all channels with given area, that which generically has the slowest approach to the long-term, periodic or steady, flow is the circular disk cross-section. (iii) Similar results for polygonal, n-gon, channels, with the optimising shape being the regular n-gon are discussed. This arXiv preprint will supplement the journal paper (submitted just before this supplement): the journal paper reports, concisely, the isoperimetric results of Theorems 1, 2 and 3. Items here additional to the journal paper include further isoperimetric results, estimates involving geometric functionals besides area such as perimeter and moment of inertia, perturbation analysis of nearly circular domains, and reporting on some previously published conjectures.