[pHaestus]

As far as overall system design goes, be CONSISTENT.

Think about what you want to accomplish first: Top performance or least possible noise? You CANT have both.

If your main goal is low noise, then you'll be undervolting 120mm fans probably and a thin radiator will be your best bet. If you're undervolting fans and using a thin radiator then you'll probably also be undervolting a 12vdc pump. If the above is all true, then you won't lose too much performance by going with 3/8" tubing, and it'll result in a more compact and clean system to be honest.

Flip it around though and say you're after max cooling. You'll be using higher pressure 120mm fans (or 160mms) and thicker larger radiators (heatercore more than likely? Thermochill perhaps). You'll be using a pump that can generate a high flowrate with a lot of resistance in the loop, and to get the max flowrate possible to your blocks you'll be using 1/2" or even 5/8" tubing.

It looks like you're kinda mixing and matching ideas and trying to do things "on the cheap". There's nothing at all wrong with that. If saving money is the biggest thing, then I'd say go with a heatercore, but a larger width so you can make a shroud and fit a 120mm fan on it. Then pick your pump based on either availability where you live or price. I really like the 12vdc pumps that are sold under various names (MCP655 I think is the swiftech one). Like Jaydee said I'd just check ebay for a newer waterblock (Swiftech Apogee, Dangerden, Dtek, etc) and buy whatever is on sale. Swiftech has clearance waterblocks too.

Hope that helps