I too had to crank the voltage up to 4v-4.2v with my LR cartos when I first started dabbling with VV, and I quickly found out why so many say that a carto only lasts them a day or so.
I found that I was far better off dropping the voltage down to 3.4v-3.5v, and then finding a juice that performed well at the lower voltage. Same thing with 3ohm cartos. By lowering the voltage down to 4.4v-4.5v I get far better life out of the cartos, and there are plenty of juices out there that work for me.