Good work on reading the stickies. There is some great info there.
That will be a nice loop. For the rads, go for the RX240 if you are running slow speed fans, or the GTX240 if you are running high speed fans. Comparison here
The Apogee, EK full nickel and Rasa all perform similarly according to this review
. The Apogee does have a lot of restriction (resistance to flow) but it will not be a problem in your loop. If you go for the Apogee or the Rasa, you will need the mounting kit for the AMD boards.
The pump is fine for your loop, the 355 is just a bit more powerful but you won't need it for a CPU only loop. If you are getting the dual bay res it has a built in pump top, no need for a separate one.
As for tube sizes, there is very little performance difference
between 3/8" and 1/2". Personally I would go for 3/8" ID (internal diameter) by 5/8" OD (outer diameter) tubing. This will allow you to turn tighter corners than the 1/2" tube and be more resistant to kinking.
Once you pick a tube size you need to pick fittings that match it. For barbs you need to ensure that the ID matches, for compression fittings you need to make sure that the ID and OD match.
Barbs need clamps for extra security. There is no real difference in performance or safety between barbs and compression fittings, if they are installed correctly. The only difference is looks and price (compression fittings look better and cost more).Edited by GingerJohn - 9/25/10 at 11:16am