The 85 mph speedo was a requirement at the time for the US market. The article doesn't make it clear whether it would actually go faster than this. It does mention that the catalytic convertor fitted for the US market heavily restricted the engine.
Because I am / was a Corvette anorak. I would like to mention the speedo being limited to 85 was a stalling measure in the US against legislation requiring airbags to be fitted to cars!!
Chevrolet fitted two speedos to the 1984 'vettes only one of which stopped at 85!!!! One was digital and the other a bar chart afffair.
John Z Delorean was also quite a key player in the Corvette program during the 70's.
I am afraid the Delorean scores a thumbs down from me