You'll probably breakdown before you make it another 300KM. Redistributing the mass is not the same as reducing it. You need to unpack everything and remove 10-20KG. Kitchen kit, books, that 3rd pair of shoes and outerwear that can be replaced by layering things you already have. While the next bike shop might be 300KM off is there an address where you can get things shipped to before then? If you are staying with the QBP family your looking for the Salsa Fargo wheel. DT Swiss TK540 36H rim, DT Spokes, Shimano XT hub. They are inexpensive and abundant. Available for $180USD mail order. If you have to carry heavy loads you should probably consider a 40spoke wheel.

My experience with a Vaya and a Bob was that above 20KG there was just a lot of wind up in the frame when traveling slowly. I think they are rated at 30-35KG, but the Vaya frame is fairly compliant so I don't think it would be a very enjoyable ride for those times when your traveling 10KM/H or less.