Then what you want may be one of the Diono car seats (Radian R100, Radian RXT, Ranier, etc.). Pricey, but not any more so than your Britax. These are also quite popular on FT.
http://www.amazon.com/Diono-Radian-C...1KYQEENVG0P833
http://www.amazon.com/Diono-Rainier-...DJ4ZNWYY067TK6
http://www.amazon.com/Diono-Radian-C...2MD81Q0GW104S0