I need to go from NY to DC for a meeting Friday morning. The meeting is at 10am at the junction of Massachusetts Av NW and 30th Street NW. Will an 8.39am arrival at IAD be ok, or should I go an hour earlier?

Also, what's my best way of getting from IAD to the meeting? Will a cab be quicker than Washington Flyer, Orange Line Metro to Farragut West, then a cab? What would the approximate cost of the cab be?

Thanks.