I had a big long reply fully explaining everything typed up. Then it seems I bounced the mouse away and lost it.
So a short reply.
SpeedStep is not bad, it's a good thing unless you have a specific problem with it. It will mean less heat thus less noise and it will save you electricity. It will have no impact on how well your PC runs. It can interfere with overclocking, so it's a good idea to disable while you find a good clock you want to run at. Afterwards it can cause crashes, so sometimes it gets left off.
In order to say if it's a good temp or not we need two temps. Idle and load. Idle is when the PC isn't doing anything. Load is the highest temperature you can get the CPU to. I'd use Prime95.
Lastly all modern motherboards should get the multiplier correct on a CPU when installed. It's unusual for them to get it wrong. To see what your SpeedStep running processor is actually running at, put the CPU under load and then run CPUz. You may well find it was the correct multiplier before you made any changes.