I've gotten a FS Pivot to sub 24 pounds and it wasn't cheap. In the end, I really didn't need such an extreme build for my uses and recently sold the frame.
A stock Pivot 429SL is about 28 pounds with XT and aluminum wheels. At the end of the day, I calculated about 4K more in parts to lose about 4 pounds, was it worth it? For me not really, but for someone who is more than a casual racer, maybe.
Since moved the parts to an aluminum frame and it sits at around 28 pounds with some of the light weight parts. No need to be a weight weenie when I won't give up the Hope brakes.