X2 5100 go to a rebuildable shock.
I was running 7100's (no res) good shocks. Just switched to Doetsch 2.2 Resivour shocks, these are GREAT shocks. Doetsch are very reasonably priced, way cheaper than fox or bilsteins.
Look around for used rebuildable shocks... I found my Fox 2.0's used for less then 1/3rd the original price and they came with rebuild kits and new oil and a buttload of shims.
Watch your local craigslist and race-dezert paulhead, its not uncommen to find pairs of 7100's for $150, and you can rebuild them for another $60 if they need it.
Call Bilstein. They revalved my 5150s. I know they also mentioned rebuilding them, but mine didn't need it. You'll have to send them to their San Diego facility.