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Your main issue is the large span for the shelves. Plugging in your dimensions into The Sagulator gives a sag of over 1/4" with pine, a tad under 1/4" with oak and around an inch for particle board or MDF.
The easiest way to reduce the sag is to have more support for the shelves. Even a single support in the middle (which reduces the span from 85&...
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