i would reconmend getting 61 for forgivness as it give access to some great drops and the battlefeild is pretty awsom combat exp but it doesnt realy make a huge difference to any other skills
i would say 48 is definatly worth it for as a first resort, the quest is a bit of a pain but doesnt take to long and the access the the pools in oo'oglog gives a major boost for when you go to gw/higher lv slayer tasks and they can realy give you an edge
all in all get 48 but if you can mannage it 61 (dragon pick drop) is worth the extra effort
hope this helps