I am not sure what's available to you as far as bikes go, but a quality bike is better than a Wartmart huffy. Those are O.K. if you only plan on using it as a once in awhile ride around the neighborhood.
The 80's are really 66-ishcc's and the 50's are 50's. If you are more than 90kg, or have hills to contend with, go with the "80".
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