Unlike the rest of the world, I find Kensington to be in the middle of no where. It is 20c suburban London, and a 20-30min trip to the Older, interesting part of the city. Look for hotels in Soho(almost none), Covent Garden, or Bloomsbury.
If only 2 days, take cabs from one thing of interest to another. Do not waste time slogging to and from the tube, unless the traffic is at a standstill.
Walk a lot.
If 2+4 days, apply the same formula.
Do not bother allocating more than 30 min for Herrod's. Just go the food court, look, and leave.