Interesting thread. I'm always fascinated to hear from people who's experience has been different from mine.
I have a Teac X1000RBL reel to reel that I bought new. It does 3.75 & 7.5 ips. I used it mainly to record classical vinyl to get long play times. Using the dbx noise reduction, high bias tape, and recording at 7.5 ips the recordings are a dead ringer for the original vinyl. The deck works extremely well for this purpose.
I also have a modest collection of about 30 pre-recorded tapes with most of them being 7.5 ips. My experience is that the best of these pre-recorded tapes cannot compete with a CD. They are maybe a little better than the vinyl version but they don't "blow away" the vinyl by any means. After reading @elliottbnewcombjr 's post I think I'll go back and try some of them again because I've had such a different experience than he has.
I've heard 15 ips tapes at a few audio shows and they sound amazing but I would love to compare them with a CD or SACD. I've got a pretty nice CD rig (Berkeley Alpha Reference II MQA, Jay's Audio CD3 Mk III) and I would be surprised if these tapes were clearly superior to an audiophile CD version.
Even though I don't play my R2R very often I love it and will keep it until I go into assisted living or die, whichever comes first. It's a beautiful piece of audio engineering and it's just plain cool.