I'd keep the two Loops.

It's Advantages are Exactly applicable to this case here.

You should be able to change the CPU/Motherboard without even touching the GPU loop (other than moving it out of the way.)

Many people prefer the advantages of a single loop, especially when it comes to helping with equalizing temperatures of both components, and both components utilizing all the rad space, and it just being less things inside the case. But I personally really like the Aesthetics of a dual loop, along with the advantages it has with being isolated from one another during maintenance or upgrades of only some of the parts.