Honest advice: don't waste your money. BC dampers are just not that good. They'll give a killer stance and generally look great, but the ride and handling characteristics are not nearly as good as you'd have with a decent set of stock-style dampers and lowering springs.
On spring rates: 10k (550#) is too much for anything short of a very good monotube racing shock that's not made in China, and too much for a DD. I have 550# springs on my car, but it's not a DD, and I wouldn't DD it as it sits. I'd probably go for an 8k (450#) front spring for a DD setup, and probably a 3k (170#) for the rears.
2002 C5 Z51. MCS 2WNR TT2 coilovers, 18x11 Forgestars, 315's, yada yada. Built Z06 T56. Bolt ons. Coming soon to a CAM event near you.
2013 F150 6.2L. 9mpg.