Thank you for the feedback, your comments are helping me narrow down what I need to go with.

I see what you mean about the mounting mechanisms, the Swiftech uses machine screws with a shoulder that screw into the backplate to achieve a consistant mount while the EK uses non-shouldered machine screws so the way to ensure a consistant mount is to check spring compression/height of arms above motherboard. I'll have to think about this one a bit, that seems slightly cumbersome compared to Swiftech's method.

The asthetics of the EK GPU blocks appeal to me more than the DD ones, so I'll be going in that direction. According to the EK website, a backplate is merely an asthetic addon, so I'll just go for the FC block.

After re-reading the triple radiator comparison on Skinnee Labs, the MCR320 is looking better and better for price/performance as you mentioned antiacid. Given the heat load I'd be putting into the loop (overclocked i7-2600K and a 580GTX (maybe a second one later), I'm thinking that a 320 mounted up top and a 220 in the bottom is the way to go.

For the pump, I was originally leaning towards a D5 vario so I could turn down the flow rate (and noise), but the MCP35X mentioned in the pump thread looks very appealing too. Not sure yet.

I'm entirely unsure as to the reservoir, I like the idea of a tube res, but since I'm planning on putting this all in a case with no window, I suspect I'll grab a bay res of some description so I can see the water level.

For filling/draining the res, a t-line at the bottom of the loop should do for draining, and if I leave a bit of slack, I think I should be able to pull a bay res out far enough to get to its fillport.

That was a good catch on the fittings possibly interfering with each other on some blocks antiacid, I'm thinking that if I go with the swiftech block, I'll do 3/8"ID tubing and if I go with the EK block I'll go with 1/2" ID tubing to avoid compatibility issues. I won't run into clearance issues on GPU blocks, will I?

I'm planning on distilled water + kill coil and/or PT Nuke despite the temptations of being able to see glowing fluid in the reservoir, the potential headaches that have been mentioned (staining, clogging, etc) just don't seem worth it.

In short:
CPU Block: Undecided between Swiftech Apogee XT and EK Supreme HF, one has the better mounting system, the other has slightly better temps when mounted properly, and accomodates larger compression fittings (ie, 3/4" OD tubing).
GPU Block: EK 580GTX Full Cover block
Rad: Swiftech MCR320 for the top of the case, if needed MCR220 for bottom of case.
Fans: Scythe Slipstream or Gentle Typhoons
Pump: Swiftech MCP35X or D5 Vario
Reservoir: A bay res of undetermined type most likely.
Fittings: Compression Fittings (Bitspower or Fesser most likely) for blocks, pump, and reservoir, and a t-line leading to drain plug.
Tubing: Clear tubing (maybe UV reactive) either 3/8"ID 5/8"OD or 1/2"ID 3/4"OD (Primochill LRT or Fesser?).
Fluid: Distilled water + PT Nuke and/or Kill Coil

The main questions that I still have are, do I have enough rad for my heat load? What about if I add a second 580GTX? Should I go with single loop or dual loop? Dual loop strikes me as more expensive to do (seems to require a second pump) but would isolate the CPU from the GPU's heat output so they could run at a higher delta T relative to air.