lets say that water is at 10 or 15 degrees.
1) would that damage the radiator if inject 80 or 90 degree hot water using a high speed pump.
2) Would that make any difference to the time it takes to heat the room
1) No.
That's what happens with old heating systems (look up sundial c-plan); they're still rubbish. Better to start the system earlier at a lower, non-scalding temperature (optimum start).
I've heard that thermal shock (sudden heating) can damage boilers on a multiple boiler installation.
2) Yes, quicker.
But the air temperature is only one factor in what makes a room feel comfortable.
