Sorry, 1am here, getting a little cranky, apologies.
I've seen a 2.13Ghz Conroe get to 2.9Ghz on stock volts and cooling. I assumed that a 1.86GHz Conroe would atleast be able to get 2.7Ghz or something around there. It will probably overclock higher, as there are few differences between the two processors as far as binning goes.