that's a respectable figure from two harvests.
The reason I do three is purely because of my altitude and location in comparison to agriculture - it also allows me to specify exactly what type of honey I'm selling.
With regard to the timing - it's quite interesting over here. After the spring harvest, if you leave it a week or two too late then they will empty the hive because there's a natural gap between the local crops coming into flower and the natural stuff coming into flower - so by removing the spring stuff when I do I'm effectively forcing them to forage further afield (where there is loads of stuff).
In the summer I could just stack supers on till August but then I'd end up with honey that was a mix, where as by doing to seperate harvests in the summer (three if the weather is really weird) then I can say with a degree of certainty that the first summer harvest is just forest honey with some forest flowers, however the second harvest I can say with certainty that the VAST majority of it will be sun flower and / or clover.
The market over here is a little more 'choosy' so being able to make these distinctions makes a difference come sales time (and there are obvious differences in the different type of honey such as colour, taste, time to crystalise, etc).