Yes Thule Racks does offer two car rack oprions for your 2008 Lexus RX350 side rails. They actually work the same way and the difference is mostly a matter of aesthetics.
The Thule 450 Crossroad complete base rack system could be turned the more utilitarian and practical purpose model. It uses the classic Thule square load bars for a more traditional look.
The Thule 450R Rapid Crossroad roof rack system is installed exactly the same way as the regular Thule 450 version, except that it uses the new sleek and aerodynamic Thule Rapid Aero load bars for a more european / premium look.
You can then mount any of Thule Racks roof mount gear carriers to the base rack load bars on both systems. All gear carriers will attach directly to the square load bars, while some of the gear carriers will require the use of Thule Xadapts to connect them to the Rapid Aero bars. This is actually a very good link to use as a reference for how each gear carrier works with the differnet versions of the Thule load bars:
Thule Racks Gear Carrier to Roof Rack Compatibility Chart