need your suggestion/expertise on my single loop pissing flow issue

[Annirak]

I think your problem is inlet restriction. A lot of centrifugal pumps can't handle restriction on the inlet. The D30's have just exacerbated the problem; they have more suction, but that just crushes the tubing and makes the inlet MORE restrictive. Looking at your tubing, I'm pretty confident that if you put a reservoir directly before your pumps (with very, very short hose runs, or pipes instead if you can do that) you'll solve the whole problem and, with that much pressure, maybe blow some gaskets)

[Edit:] I don't think the CPU block will cause a problem once you fix your inlet restriction. You might even be able to get away with a single loop.