Since you want a smaller radiator and a quiet system see if you can get a Black Ice Pro 2. I know it's a double 120mm radiator however you can run a couple 50CFM fans in near silent operation and have great cooling capability for a well overclocked processor and even graphics if you wish. I have one on my prescott and 9800, it works great and around 9v on my 2X Delta 3-Blade 120mm's they are completely silent.
In addition to a larger radiator for a quiet computer you should look into a few other quiet parts. A good pump, if you can still find them, are the DDC-12v or MCP350 11w pumps. They are basically the samething however with a different label. There are 18w versions out there however are a tad louder, consequently they are more powerfull though. I'd recommend an 18w if you have more then one block, larger then a double 120mm radiator and more then a few meters of tubing. A good block for a low restriction system is the Swiftech Apogee. From its base design it offers great performance for the buck and very low restriction with a low required flow rate. This makes it a good choice for the DDC 11w pump because despite it's high pressure capabilities it somewhat lacks flow rate due to it's restrictive compact design. Another thing to consider is tubing size, personally I swear by Tygon R3603 7/16ID (11.1mm) x 11/16OD (17.4mm). I use it in my system and I believe it's the right balance between flow rate (up to 10L per minute) and size. It has a massive 1/8 (3.175mm) wall so this tubing can really take a sharp bend without kinking plus doesn't hold shape after a long period of time so it's easily reuseable if you want to redo your loop. It also can go over 1/2 barbs and because it's a little bit smaller it creates a better more leakfree seal.
So for a very quiet cooling solution I would suggest you buy some kind of GPU block (unless you already have a quiet air HSF), the Swiftech Apogee, a double 120mm radiator, DDC-12v/MCP350, 7/16|11/16 Tubing, and a couple of 120mm fans around 50-75CFM. I guarantee with that setup you will be very happy.