Santana's 'Black Magic Woman'. Even when I had the finest Hi Fi at the time and the best quality imported quality record it still falls short of what we are hearing now. Imagine this re recorded today with all our magic now.
Of course it still does not detract a bit from the original version which we all know and love so well.
Hendrix 'Are You Experienced' could have the modern recording treatment and I think it will sound killer now too. But albums like 'Dark Side of the Moon' hit the nail for me fidelity wise at that time too which was pretty amazing when you think about how other albums were sounding around that time too.
Being a hi fi enthusiast in the 70's listening to very high end gear and being around others who had great listening skills was interesting at the time. There were larger discrepancies in terms of hi fi sound from various albums around at the time. Nashville were already turning out magnificent acoustic and country sounds by then.
And of course electronic music was already sounding very good in that period too. Bypassing microphones and recording things direct meant being able to create a very high quality picture.