33 vs 45 speed quality

On the outer grooves of a 33 there is no real advantage to the higher speed, although 45s might sound better for other reasons simply because they are produced for the audiophile market. However, as the pickup moves to the inner grooves the speed of the vinyl passing the stylus becomes very marginal for sonic quality. Cutting the record at 45 rpm preserves sound quality at the inner grooves (although using 33 rpm and just not recording anything on the inner part of the disc would yield the same result and playing time). 45 rpm was invented for the singles, which were all inner grooves.

Maybe your system is not wide-range enough or dynamic enough for you to tell the difference. There definitely is an audible difference. Record companies don't record at 45 rpm just to take up more space on the record (and charge you more on top of that).

Are you comparing versions of the same recording(s) on 33 and then 45??? If so, then you could have reached the limitations of your playback gear... or your ears.

45 rpm versions of audiophile lp's are more about 'old wine in a new bottle' than great audible differences. i have worked in the music business since the 1970's and unless the lp pushes the limits in terms of 'total time' a 33 sounds pretty much the same. also albums were meant to be played uninterupted through each side(any artist, producer, or engineer would agree).....changing discs to accomodate 45rpm destroys the magic of continuity......god bless classic vinyl for staying in business even though these tricks won't play with everyone.