Can only assume you are speaking on the DCS Pro back variants...
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As far as long exposures? I doubt you will have much success with anything longer than 2 secs with this generation sensor. I recall Phase getting longer exposures using the Kodak chip, but nothing to compare to the latest generations.
FWIW, few DSLRs can give you clean looong exposures that compare with your Kodak 14n/SLR.
good luck,