Ciao
non sono mai stato in Islanda ( partirò a metà Giugno )ma a proposito di questa zona ti riporto ciò che dice la guida ( ICELAND ROAD GUIDE ) :

... STORISANDUR ,west of Rettavartn lake the Skagfiroingavegur route continues to the east to Grettishæð.From there it is possible to drive to Grimstunguheioi in Vatnsdalur valley. This route is very slow with larged rocks on the road. Not passable for small jeeps.By Grettishæð is a route to the south and the east through Krakshraun and east to route F35 Kjavelgur. This part of route is also slow...