Thanks for the replies, guys.
So first off, the stock heatsinks. The fin spacing isn't as generous as my Ultra Extreme 120s, but I'm not sure its terrible.
A shot on its own:

A shot with a monitor behind it so give an idea of the space between fins:

Up against an Ultra Extreme 120 for scale and compaison:

None of my attempts are really fanless, just maybe not having the fans directly against it.
So here are some baselines. I just install Ubuntu 12.10 server on it, outfitted it with 6x 450G 15k SAS drives in a raid 5 with hot spare, and updated it to current. Its about 72F in the house, roughly 22c. With nothing running, lm-sensors reports:
i5k_amb-isa-0000
Adapter: ISA adapter
Ch. 0 DIMM 0: +55.0°C (low = +105.0°C, high = +124.0°C)
Ch. 0 DIMM 1: +50.5°C (low = +105.0°C, high = +124.0°C)
Ch. 1 DIMM 0: +50.0°C (low = +105.0°C, high = +124.0°C)
Ch. 1 DIMM 1: +47.0°C (low = +105.0°C, high = +124.0°C)
Ch. 2 DIMM 0: +53.0°C (low = +105.0°C, high = +124.0°C)
Ch. 2 DIMM 1: +52.0°C (low = +105.0°C, high = +124.0°C)
Ch. 3 DIMM 0: +59.0°C (low = +105.0°C, high = +124.0°C)
Ch. 3 DIMM 1: +51.5°C (low = +105.0°C, high = +124.0°C)
coretemp-isa-0000
Adapter: ISA adapter
Core 0: +42.0°C (high = +84.0°C, crit = +100.0°C)
Core 1: +37.0°C (high = +84.0°C, crit = +100.0°C)
Core 2: +46.0°C (high = +84.0°C, crit = +100.0°C)
Core 3: +37.0°C (high = +84.0°C, crit = +100.0°C)
coretemp-isa-0001
Adapter: ISA adapter
Core 0: +46.0°C (high = +84.0°C, crit = +100.0°C)
Core 1: +41.0°C (high = +84.0°C, crit = +100.0°C)
Core 2: +43.0°C (high = +84.0°C, crit = +100.0°C)
Core 3: +42.0°C (high = +84.0°C, crit = +100.0°C)
The 4 CPU fans are spinning at 7200/7350 rpm, and my iphone says its 70db at a distance of about 1 foot.
I will follow up shortly with results from actually generating a workload.