Fed uses natural gut in the mains with Alu Power Rough in the crosses. He strings in a range of high 40s to low 50s depending on the opponent. The more of a heavy hitter his opponent, the higher tension he uses to control the power.
Personally, I use K gut pro in the mains at between 56-60 with Alu Power Rough in the crosses at 2lbs lower than the KGP. I find that with the KGP in the mains, the feel for volleys and touch shots is a lot better. At 60/58, playing about 5 times a week, 2 hours each time, the set up lasts about 30 hours before the mains break. Playability remains relatively unchanged for the whole duration before the KGP breaks. With APR in the mains, I find there is a little more power, however finesse and touch shots are hard to pull off and after about 5 hours, the drop in playability is noticeable. Having said that, the set up has lasted 50 hours with moderate fraying on the crosses. For both setups, spin generation is a little more pronounced with the APR in the mains. However having APR in the crosses seems to give some side spin on ground strokes especially slices. This could of course be an effect of my stroke. All in all, I prefer the KGP in the mains and APR in the crosses set up a lot more.
Currently, I am trying to go to lower tensions to see if that increases the lifespan of the setup. However anything below 56 in the mains and I have problems with control.