I was not lucky enough to see the original cast in London, but I did manage to watch Sarah Brightman and Michael Crawford perform in the 1988 Tony Awards. This is available on YouTube to watch.
I owned a double cassette tape recording of the original London production and listened to it over and over again often joining in the singing. Sarah's voice is beautiful and she inspired me to sing "Think of me" in a local eisteddfod when I was 17 (1988 too). I have seen the theatre show three times now, once in Sydney (Australia), once in the Albert Theatre in London and once in Brisbane (Australia) but all with different casts.
I've also enjoyed listening and watching a televised version of "Song and Dance" also composed by Andrew Lloyd Webber where his brother Julian Lloyd Webber plays cello and Sarah sings. If you like listening to Sarah in Phantom, you'll also enjoy her voice in Song and Dance.
As for Cats, I had the originally Australian recording which didn't include Sarah. I did get to see Cats in New York in the week it finally closed on Broadway in 2000.