55°C is perfectly fine for full-load CPU temp, so if you can slow down the CPU fan some more it'll be a bit quieter without risking overheating. Anything over 70° is not recommended, but mid 60s are alright. Remember, the CPU won't normally be running at full load for extensive periods of time in normal use. It's normally a tradeoff between cooling and sound; the better cooling you want, the louder it's going to be. Of course, water cooling is an exception to this - it's very quiet but cools very well too. My temperatures (in a nominal 16°C (60°F) room): Idle: System:20, CPU:27, Vid:don't know exactly, heatsink feels slightly warm (fanless GeForce FX5200) Full: System:25, CPU:52, Vid:probably ~50° - heatsink feels very warm But I have a total of 12 fans, so it's not exactly quiet...