I just called Capital One Retention 1-800-889-9939 and got the interest rate on my gold card lowered from 20.36% to 15.39%. I also inquired about a limit increase, she said since I got my last one in Nov, I would qualify at 6 months for a "large" increase. Now I have some leverage for my other accounts.
Good job! I called also.. they upgraded me to a gold card, and gave me a $200 increase. I had a secured $49/$300 limit, one over limit (they waived the fee), open about six months.