Right now it's all at stock. I'm having some weird problems with my video card (that I've had since I've purchased it) so I might OC this system a little before sending the card back to XFX to get it checked out.
Here's my explanation for the split, and 'T's:
Originally I did look into 'F's and Y's, but I couldn't find any Y's that went from 1/2" to dual 3/8"s, and like you already mentioned the F's are useless unless it's specifically for swiftech stuff.
Second, I did a little math work. A single 1/2" diameter tube has an area of:
(1/2")/2 = 1/4 this is the radius
(1/4)^2*pi = area
area = .196
Dual 3/8" tubes have a TOTAL area of:
(3/8")/2 = 3/16 this is the radius of ONE tube
(3/16)^2*pi = area of ONE = .110
area * 2 = area of both
area of both = .220
.220/.196 is roughly 12%, which means that having 1/2" to dual 3/8" tubes drops the pressure/speed by 12%. They are so close to being the same.
Next, the motherboard tubes look very small, definitely not 3/8" tubes, they're tiny metal pipes. If the pressure is too high going in there, which I have heard high flow systems have had, the tubes could just pop off and I would be left with a destroyed computer. So basically what I did was I made an "offramp" for excess water. I'm not too concerned with the NB/SB since it cant cool itself normally without watercooling, so the watercooling is just a bonus. Also, the outflow from the 'T' where the two 3/8" tubes reconnect give the 1/2" no pressure differences, allowing for the whole system to be unaffected by the motherboard loop. (also the motherboard hose connectors are so close together that I can't use
real clamps, I have to trust ASUS with they're ones.)
How's that sound? It convinced me!