I use K90 with RPM 17 mains (35-43lbs) with either VS Team 17 (42-48lbs), Klip Legend 17 (40-45lbs), Performaxx Whisper Touch 17L (40-45lbs) crosses.
I like the RPM at lower tension but most of the natural gut are too powerful @ 40lbs or less. The Klip Legend is lower power (stiffer) and handles lower tension stringing better. The VS and WT are quite powerful and with my skills (or lack thereof), I find it harder balance power and control. That said, on a heavier day, that power comes in handy.
I'd put the Performaxx whisper touch in the same power zone as the VS Team. Since I'm using the 17L (1.2mm) WT, it's thinner than the VS Team 17 so it is that bit more powerful and has a bit more bite. Feels great too.