all great points.
My Tubus Tara front rack weighs about 500, 550g and many other front racks like the Trek or Surly are just physically much bigger (but have upper flat platform part, that I dont use) and are heavier. I can't find the weight of the Trek rack, they are coy it seems about its weight.
The Trek 520 back rack is 800g. I cannot find the weight of the front rack but I am guessing 600g. These come with the bike so I will not be replacing them