I did some searching around on the website and I'm was originally wanting x2 18's in the back of my tahoe but I noticed 15's would probably be the better chose?

18's
http://caraudio.pgpartner.com/search...asterid=412358

15's
http://caraudio.pgpartner.com/search...sterid=8028861 (whats the rms?)
http://caraudio.pgpartner.com/search...terid=21528720
http://caraudio.pgpartner.com/search...terid=10333817

85+ dB should be plenty correct? (still learning)