There is indeed quite a bit of research that suggests that anything more than cd red book is unnecessary, but also some weak indications that a bit more might just make a tiny difference, but only just. Since the resolutions of Bluray and SACD are both well above this, there is no chance in the world that you can hear any difference between these two higher resolution formats.
There are two caveats, however. The first is that for recording purposes in the studio, working in higher resolution makes life a lot easier. But that logic does not apply to the distribution format.
The second is that for comparison you really need the exact same mastering/recording. SACD or Bluray is often mastered differently from red book discs, with a wider dynamic range etc. So you are not necessarily comparing like with like. And of course you need material that was recorded in high resolution in the first place. Using an analogue tape as a source is meaningless. If you want to do a meaningful comparison you need to use the same high resolution file, and downsample it to 16/44 for comparison. When this is done, differences have tended to disappear.
In practical terms, the choice between SACD and BD is simply a matter of practical convenience and availability. Fortunately a great player like the Oppo 205 will play all of these formats, so you do not even have to choose. Just have your cake and eat it. Enjoy the music.
