Personally I will only buy pants 20K or higher, although 15K+ is probably sufficient. I definitely wouldn't go any lower than that unless you plan to buy new pants every season, use waterproofing wash/spray regularly, and don't do much hiking/sitting/falling.
16 Gnu Swallow Tail Carver . 16 NS West . 15 NS Snowtrooper BIA
16 Burton Genesis X . 15 Now Drive
16 Flow Talon . 14 Flow Hylite