1k feet is not the measure, it's 300M (984ft)... which I feel the tallest tower will definitely be above.
Never seen the Perkins+Will design, but generally two inward tipping towers connected with a skybridge would look sharp
The Emirates Tower Design would add some variety
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Or the Absolute Towers?
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Maybe even more twisty like Panama's F&F?
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More perhaps minecraft style like Bangkok's Mahankhon?
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Ugh, who am I kidding they will likely be pretty dull, but as noted there's been a lot of exciting skyscraper / development news in Chicago. Tribune's monster, One Chicago Square, WP South, OBP, NEMA, the 78, etc.