I say GO FOR IT! I thought about this setup too. I have a set of 5100s waiting for install but I can't decide what to do. Stacking the RC 3" kit on top of Bilstein 5100s set at 1" is a fairly new setup that peeps are starting to do so it's kind of in that trial and error phase ($icktitan was 1st IIRC). I think you'd be the first pre 08 4x4 w/ the 5100s set at 0 w/ 08 coils and the RC 3" kit... It'd be pretty cool if you were the guinea pig and reported back! From my "calculations" it'd be something like 3.25"-4" of lift w/ that setup.
Leveling a pre 08 4x4 w/ 5100s and 08+ coils is about 1.5" give or take
RC 3" kit gives you about 2.5" give or take
Now we have to wait and see how the RC UCA perform with the stacking. I want to know how they handle the 3"+ of lift (coil bucket contact, droop, travel, etc.). If the more expensive UCAs (PRG, Camburg, TC) handle this better I may go with a frankenstein setup. 5100s, 08+ coils, spacer & PRG UCA... or skip the coils and go w/ a taller spacer.
BTW sorry I didn't answer your ?
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Adjustable shocks