D and Gr and 737man, I quite agree with you that it does people good to see what happens on the other side of the radar screen, and even my 'low cost' company has done this with pilot visits to our local friendly ATC unit. Unfortunately, we are now unable to reciprocate in the current security scene as no-one, and I mean no-one is allowed on the jump seat apart from operating crew. Not positioning crew, company people on standby, or even the Captains family.
In my Company, we like to fly FMC econ speeds. Unfortunately in the NG this can give a speed of 263kts, so we have a standard descent speed for busy airfields of 280 kts.
Our Company procedures forbid us to exceed 250kts below F100, unless specifically requested by ATC. I think, possibly, this 300kts business is more a case of people wanting to get home a couple of minutes earlier - but then I could be wrong!!! There are an awful lot of different types and I doubt an ATR could match a 747 even in the descent at econ speeds.