3.4NM - plenty of space. We do quick backtracks (our taxiway is approx. 600 metres from the threshold) on a regular basis, with a/c at 7NM.
99% of the time it works and everyone's happy (a/c launch 3 to 4 mins earlier, pax get home quicker, less fuel used etc.)
Must admit, I agree with 1261 and Dan Dare completely.
Oh, to be paid peanuts, that'd be a step up!