Hi!
I have used the Telex 750 for many years in Cessna 421s. It was the ideal headset for that aeroplane which is quiet enough to fly without headset. You really forgot you were wearing a headset after a few minutes. For turboprops and single engine piston aircraft it does not offer enough soundproofing.
Since many years I exclusively use a Sennheiser NoiseGard headset, it must be the predecessor of the current model HMEC 26. It is a lightweigt closed headset with active noise reduction. When flying on propeller driven aircraft I turn the noise reduction on, in the Citation I leave it off. I used that headset also in my brief time flying a turboprop (the Metroliner, probably one of the noisiest civilian cockpits) and found it just sufficient.