BA @ LHR: The new "T5" is between the 2 runways, so this is not a factor. T4, that we are moving out of, is very much better for the South Runway. However, the runway alternation at LHR is strict, and there is little chance of using it out of sequence. ATC are aware, and when permitted / available e.g. landings on 09R, I would leave it to them to offer - as you say, ATC know which is better.
While on the subject of requests....why do you need to know your parking bay at 120 DME....?
Depends on airport, but can affect Pax Handling e.g. Wheelchairs v Highlifts, connecting passengers, Ground Power etc. The Taxi in and parking is part of the approach brief, so if the information is available prior ToD we ought to seek it out...
NoD