8 track and open reel are completely different animals and don't compare to each other at all. As far as fidelity is concerned, 8 tracks mostly suck. Badly. And that's mainly because it's nearly impossible to maintain any proper alignment from the tape to the head, since 8-track shells which aren't very precision in the first place, have the pinch roller built into them. And alignment varies wildly from cartridge to cartridge.
Open reel on the other hand has the capability of very high fidelity, if your deck is maintained and aligned properly. If not, you could experience anomalies like overly fat bass or rolled off highs, etc. If the deck's set up properly, it should produce a recording that's pretty close to the original in terms of sonics. Technically, an open reel deck should be more accurate than cassette. I say "technically" because I've heard some excellent cassette decks that could give a good open reel machine a run for their money.
If you've experienced sonic coloration with an open reel deck, it's because there was a problem with the deck or the tape. 8-tracks sound colored just because they're mostly garbage.
Your cassette dubs you borrowed could have been muddied by a misaligned deck, but they could have also been damaged by the elements or magnetized.
Cheers & good luck,
Bobbo :-)