Yes, you always use the top tether whenever you can -- whether you are installing your car seat with a seat belt or the LATCH belts.
Please keep in mind that you can only use SuperLATCH to the full limits of your Radian if your
car was manufactured after September 1, 2005. Often times, even if your car's model is an '05, it was probably manufactured in the previous year. To be sure of when your car was manufactured, open the driver's door and there will be a white sticker (where your tire pressure and such is listed). Your car's manufacture date will be found there. If your car was manufactured before 9/1/05, then you must stop using LATCH as per your specific vehicle's LATCH limit (which should be found in your car's manual).
ETA: I thought I remembered a post by you, and sure enough, I did! You have an '07 Camry, correct? In that case, you should be able to use the Radian with LATCH to the full limits of the car seat (again, always double check the car's DOM before you continue to use SuperLATCH). For future reference, or if you ever plan to install any other car seats in your vehicle, Toyota states to refer to the child restraint's LATCH limit. Also, you only have LATCH in your outer seating positions, not the center.