Unless you actually want WOCK-CD (
http://en.wikipedia.org/wiki/WOCK-CD) or "Franken-FM" WKQX (
http://en.wikipedia.org/wiki/WKQX-LP), skip the large, all channel antenna.
The math says that the C2V will work at your location, however, an attic location always introduces a large amount of error into the forecasts because of the attic environment. Your attic might do fine or it might not. Being prepared to placing the antenna outside so that it has a good, clear view towards downtown Chicago will go a long way towards improving your odds.
Survey your location for any spots that are free from common obstructions such as trees or neighboring buildings in the direction of Chicago. Give consideration for those locations when installing the antenna.