I am thinking about the M Eastpack trolley (78 liters). I just thinking whether that is enough packing volume for a longer stay(for all the stuff)? The Rimowa salsa multiwheel 73cm and the Travelite Crosslite have both about 86l-94l.
Or should i go with thew 121liter eastpak trolley? The 121 liters volume seems absolutely huge to me and I am scared that I will easily exceed the limit of 23kg. But the M trolley with 78 seems to small for my needs? Does anybody know what the volume information really means?

Yes I looked at the all the deuter backpacks. They are very good for trekking but regarding carrying a laptop and university stuff around all the time, they are just to small. The backpacks are always full with high-tech stuff for the carrier which i don't really need and that adds always weight. The Eastpack goof can expand to a maximum of 47 liters=)

I am already weighting the stuff I definitely take to china to not suffer a surprise