Main system's spec is in sig.
Just to add, Sonar is on it's own dedicated setup (dual-boot Vista 64bit). Drives are a 500 GB WD Black for system (also swap, in 8GB partition at start of drive) and a 500 GB Samsung F3 for audio streaming (1st partition on that drive, 250GB). USB memory stick added for 4GB "Readyboost" swap space.
Cooling by single case fan at rear, single fan on cpu, both 120m slow-running Noctuas. Big Noctua heatsink on cpu.
GPU has standard fan, but with card's BIOS edited to reduce the pre-set rpm curve to what the card actually needs (as stock fan speed started at 65% at idle and ramped to 100% by 50 degrees C. Noisy like a vacuum cleaner).
Both drives in QuietDrive cases.
PSU is a 600W Corsair, very quiet indeed. RAM also Corsair, running at factory clock and voltages - in fact, nothing overclocked.
System is home-built (I've been building PCs since 486 days), runs cool, is very stable and very, very quiet unless running a 3D game which ramps up the GPU fan.
It's not state of the art, but powerful enough that I don't currently feel the need to upgrade anything.
It can run X1C + the version of GR that comes with X1 without really noticing it - cpu loading about 4% peak.
My 2GHz Core2Duo Centrino (I forget which cpu model no.) 32bit Vista Lenovo laptop with 2GB RAM and a 5400rpm HDD plus on-board graphics can also run X1C + GR, peak cpu loading about 15-20%.