I'm sure we all know it costs to get bikes lighter. But you can drop some weight in the wheels, you can drop weight on dropper posts (PNW makes a decently light one), you can drop weight with cranks (Carbon or Titanium), and of course tires. Some weight can be dropped in the shock, DPX vs X2 or Rockshox Delux Ultimate. Also, XTR is lighter than the Sram Transmission but its not offered in build kits. Oh yeah, XTR brakes are also lightest last I checked. I don't now, I doubt we would see an SB160 under 32 unless its a small with all the high end goods.
Crazy to say the Hightower is lighter, I used to think my Hightower was heavy and that frame over beefed up. But all things being equal, I'm sure the SB160 is a lighter frame in comparison to the Megatower.