Well, I have several systems running fully or partially passive and external/passive has it's plusses and minuses.
The massive plus is that these systems tend to run extremely quiet or silent.
The 'minus' is that you have to change your mindset from one where low temperatures are the aim, to one where you basically ignore the system temperature because the system is stable, so why worry what the temperature of each core is?
A single Zalman Reserator 1 will easily handle that CPU, in complete silence. It will run at about the same temperature as a decent air cooler, but without any fans at all.
A single Zalman Reserator 2 will handle that CPU and a top modern graphics card (GTX 280 or HD4870), also in complete silence.
A Zalman Reserator XT will do everything a Reserator 2 will, but it also has a fan option to provide additional capacity for a second graphics card. The big downside with an XT is that it has fans in it, so it makes a noise.
The system below has a heavily overclocked Q6600 on one tower and and the DFI X48 motherboard northbridge and crossfired X1950 Pro graphics cards on the other. There are two fans in the case, but they never come on. It runs as cool as an air-cooled system, but it's silent.
This Lian Li S80B has been fitted with an Innovatek Passiv radiator
and then it's got a Zalman Reserator 1 plumbed-in in series to give a massive reservoir of water.
That one has a Q9450 at 3.8GHz and two HD4850's in it. And you can't hear it at all.
My preferred system at the moment is a Zalman Reserator 1 with the pump removed, a decent CPU block, a Laing 10W DDC, a 120mm radiator with a fan linked ot the CPU header and 3/8" tubing. That's near as darn it silent and it has more than enough capacity for a heavily overclocked CPU. The CPU fan comes on only when required when the CPU is absolutely maxed out. And you can pick up second-hand Zalmans for about £70, which is a huge amount of metal for your money.
