Hey, man. I am also in NYC. Recently inspectors got more strict on grounding services here. Although there is a couple of ways to ground service recently everybody here installs a grounding bar like this
http://stormcopper.com/design/Electrical-Ground-Bars.htm
next to service and terminates wires there with copper lugs. Anybody, please, respond if regular lugs are code compliant.
This works for all sizes of services. See 250.54(F)(3).
Run Your GEC to water pipe within 5 feet - size depending on service conductors (table 250.66) - green #8 for hots #2 and smaller.
http://www.safecoelectric.com/images/resources_pdf/NEC2008 Table 250.66.pdf
If you sleeve it with emt you have to bond conduit on
both sides with fittings and same size green wire.
http://forums.mikeholt.com/showthread.php?t=144690
I would run 2 GEC taps from bar to each panelboard (2 in your case) with service switch and terminate them in neutral bars.
Of course keep the green screws at neutral bars tied to enclosure
Bond service raceways and enclosures with same size green conductor. Avoid paralleling Neutral conductor.
Run #6 to ground rod - supplementary GEC required here in NYC. Nobody asks here to check for 25 ohm or less resistance. Can anybody answer if it should be 25 ohm or less or second rod driven?
Some inspectors would ask to provide Intersystem Bonding Terminal but for most the copper grounding bar is enough for other utilities (telephone, catv, dish) to tie their grounds. Just attach to bar 3 extra spare lugs.
Ask more questions if needed. I am happy to answer as I was answered professionaly many times on this forum. :thumbsup: