I actually came up with a figure of well over 200,000 for Sel-kai, when comparing it to Venice in terms of size and then multiplying that size difference by Venice's population. It's substantially bigger, probably well over double the area, and at the sort of time I was looking at Venice had an estimated population of over 100,000. Being bigger, Sel-kai's population density is probably lower though.
Something similar happened for Haalkitaine when comparing it to Paris. Again, the land area covered appeared substantially bigger, being about double, and the population of Paris was probably 50-80 thousand. Assuming 50 within the walls, that would put Haalkitaine at over 100,000.
I read that medieval cities tended to have really dense populations - no-one had cars to get around for one thing.