If you were travelling long distance it might be worth draining the loop, but for a 10 minute drive it should be fine.
I got the RS360 kit, but that wont change anything. Once you have enough rad space, more doesn't do anything.
Before I got the water cooling, my 212 EVO was giving me 25°C at idle and 65°C under load. After the water I was getting 15°C idle and 45°C Load. Ambient temperature must have been fairly cold, guessing somewhere between 5-10°C.
You can read my build log (in my sig) for more information on my loop and how it was made.