Some interesting stuff here. How a blanket 270kts can be imposed is beyond me.
As has been mentioned, if everything comes over over to the TMA sector at 270kts (or 300 or 250) no matter what the grouping, then that is not speed control - it's a mess which may require dog-legs, speeding up and slowing down of certain aircraft. R/T loading is increased and fuel is actually wasted not saved.
If the En-route sector has to get everything at 270kts and in trail then that could be a lot of work (especially if their hands are tied with the speed). If there is no holding it's wasted R/T time (and in the LTMA especially it could actually lead to wasted runway utilisiation). If there is holding it may not help TMA out enough.
The only thing I can think of for introducing it is tenuous:
If an aircraft meets the Standing Agreed level between En-route and Terminal, as well as being at 270kts; the TMA Tac can ask for the aircraft to increase speed and get a slightly better rate of descent or reduce speed on an aircraft, and with less speed to lose, their rate of descent won't be as bad for as long as it would be reducing from 310kts+.
I'm at MACC and would hate to see this 270kts come in for us. The presentation between TMA and En-route is getting better all the time and we are speaking to each other more about sequencing.
I think the key to all this is awareness of what the receiving guy is trying to do as well as understanding the possible difficulties the offering guy may face in trying to help.
Being aware of other sectors around you whilst you are busy yourself is an art - possibly even a luxury you can't afford when things are really hot.
As a Tactical at MACC, when you're busy, it means you need a good Planner at your side.
And/or good coordination between TTM/GS/LAS/Bank Sups? (4 centres 4 names!) can help. This has to be done with reference to the radar/TSD, workloads and the other stacks being fed at the relevent airfield.
Until we get arrival manager tools which tell us on the radar what speed to assign from medium to long range, we'll all have to earn our corn Controlling and that includes choosing the speed which suits us, adjacent sectors and as many aircraft as possible. That speed is not a blanket 270kts. Good luck and pardon my input on matters LTMA!