I have the Sin, live near Tahoe. I've only been on the Sin for 2 days so far; have been working on the Volant FBs in the deeper snow we've had recently. :-)
My fiance has a K2 T-Nine from 2003 or so (blue & gold color scheme), in about a 160-165cm length. The Sin in 175cm is much heavier to pick up & carry than her T-Nine, FWIW. That's about all I can offer for a comparison to the K2s.
My other ski for the season is a Salomon Scream Pilot Hot, also 175cm. I love that ski on the hardpack -- goes as fast as I can make it, and does not chatter one bit. It bounces somewhat on frozen crud, but not uncontrollably. It's much smoother than my previous Salomon, a Scream Pilot 10 from about 2002. It prefers running at (at least) a slight turn; straightlining starts the tips wandering a tiny bit; keeping it on edge feels more stable.
I really like the Sin in Sierra snow. It handles much easier than the FB on all conditions, but doesn't float as well. It goes through crud better than the Scream Hot, as it should, since it's heavier. Edge hold on hardpack seems about the same as the Hot, but I haven't been on it on truly hard conditions to compare. The Sin is by far a better choice for an all-around ski than the FB: more maneuverable, easier to control, edge-to-edge on hardpack was great. I didn't notice much difference in the quickness of turns between the Sin (81mm underfoot) and the Hot (75mm underfoot). The Sin straightlines amazingly well, or will turn when you want - either way, it feels really confident and in control. The FB was more difficult to straightline, and definitely is nowhere close to a carving ski -- you can ski it on hardpack, and it holds an edge fine, but it isn't all that fun on hardpack.
Overall: The Hot is light & forgiving. The Sin is moderately heavy, but controllably so; less forgiving than the Hot, a bit more snappy than the Hot. The FB is heavy, sometimes difficult to control for me, not forgiving at all compared to the Hot or Sin.
FWIW, the Hot was mounted with the Solly 912 bindings it came with; the Sin and FB with Look Pivot bindings.
Hope this helped some... comparing 2 skis you didn't ask about, to the one you did...