If you're driving to McLean from McLean/TC/Falls Church/Merrifield, you're not dealing with "DC traffic". Driving from between Rosslyn and Ballston, or Reston, is a somewhat different story and it sounds like you'd be happier Metroing in that case. And, yes, National Airport is convenient to Metro; Dulles Airport, not so much, for a few more years.
I agree with Ber2dca on the plusses of Rosslyn-Ballston; the minus is that you're further from work. Sounds like you're ok with that.