OME Medium, that's what I did and LOVE it!
The only difference between the OME Med. & Firm lift is the actual height of the spring, the spring rates are the exact same. I don't need the additional height or caster issues so I went with the Mediums, me likey a lot!
I put the ARB bumper on before the lift and you don't want to use spacers the ride sucked and the body roll was terrible. I bought the OME Med lift from Mark at MetalTech, those guys are awesome!

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President -
TLCA South Sound Cruisers
2007 BC, 4x4 AT,Rear Locker, A-Trac, Terra Grapplers, BudBuilt Skids, Stubbs Sliders,
OME Med/Med, ARB Bull Bar, IPF Fog lights, ICom IC-208H 2M/440
TLCA# 16640