Did you just acquire them or have you had them a while? My fav at the moment in the standard length (I have four) is Mayami's Big Spin mains with YTek Oct Twist green. Another fav hybrid is FireWire mains and Strike Force Rip crosses. Thanks for reminding me that I need to string up the 27.5 (only have one) and play with it a bit.
When I was using the PSL I played with either Kirschbaum Competition at about 48-52lbs. depending on time of year, or more recently Spiky Shark around the same tension. I'm not sure which string I liked better, but they were both good. If I were stringing it now I'd try something more along the lines of my current setup I use in my Rossignol, Ultra Cable at 50/38.