MC14 ramsinks are TERRIBLE. They don't stick to jack.
Enzotech BMR-C1 sinks are much better and cheaper.
Black Ice Xtremes are alright rads. Swiftech MCR220's are a better choice though since they are cheap and work great. I recommend a tripple 120 rad, the MCR320, though for those 8800's. And probably another triple 120, MCR320, for that quad. Those are hard to keep cool, even under water.
What pumps are you using? You will most certainly need two pumps for a loop like that.
I'd go with 7/16" ID 5/8"OD Masterkleer tubing.
Swiftech Microres is a much better res.
Why are you using a Y- joint? Why not just use two seperate loops.
Pump > GPU1 > GPU2 > rad > pump?
Pump > CPU > Rad > Res > pump.
Or do some kind of y-split for the res so the two loops can share the res.
I can't help but chime in here.
First, since when do you need TWO MCR320 rads to cool a quad and 2 gpus? And since when are you going to need TWO pumps? A single MCR320 will cool that setup all day long very well, and a single MCP355/DDC3.2 will do the job all day long. You are only talking about having a Fuzion block, which is about the least restrictive block on the market, and two VGA blocks and a rad. A single MCP350/DDC3.1 will do the job for that matter.
The MCP350/DDC3.1 is the uber-quiet pump to get if noise is a concern to you. It has a bit less head pressure and flow than the 355, but it won't make a difference with the parts you are looking at. If you use 3/8" tubing then this will work well as the MCP350/DDC3.1 and 355 both use 3/8" ends. If you want to get more performance and use 7/16" tubing with the MCP350/DDC3.1, get a
Petrastechshop top. It increases the flow of the pump a lot. An MCP350 with Petras top is my weapon of choice for both quiet and performance. Others prefer the MCP655 as it has more flow, but it is also louder and larger.
The Swiftech MCR rads perform better than the Black Ice rads for the same cost. Get an MCR320.
As for the res, do not get the Thermaltake aquabay. It has aluminum in it which is best avoided. Stay away from ANYTHING Thermaltake when it comes to watercooling. Their products are made for bling but suck when it comes to quality. Go with a Swiftech Microres. It is made well, is small, and can mount almost anywhere.
The tubing is really a matter of preference. 3/8"ID 9/16"OD tubing with 3/8" barbs is going to be very easy to work with but does require good tight clamps to hold well. The 7/16"ID 5/8"OD with 1/2" barbs is about the most efficient in terms of tubing sizes, but it takes soaking the ends in hot water to get the tubing onto the barbs. However, once it is on, it isn't coming off. I personally still use hose clamps regardless.
As for the Y, this is a common misconception. In by far most cases, running everything in series is the preferred way to go and yields the best results. There is only about .5c temp difference or less in the water across an average loop, so loop order isn't very critical when it comes to temps. The ideal order is res-pump-rad-cpu-gpu-gpu-res, but it is the best choice just to use the easiest tubing routing that will naturally run the fluid so that air will bleed easily into the res.
Having two loops for this setup is total overkill. One loop with a MCR320 is what you need.
I would probably get at least the pump and rad from crazypc.com as they have very good prices. Petrastechshop is also a favorite. If you go with 3/8" tubing, you can just get the Masterkleer. If you use 7/16", I would probably go with Tygon R3603 as it stretches a lot easier than Masterkleer does.
