Groth offers good advice, that's the way to go regarding a full radiator solution.
If you still care to look into dual heater cores: Fedco #2-342 / GDI #399090 this is about the largest single pass heater core. A pair of these will offer the lowest resistence you can get for that monster pump. This rad is large enough to take 2 x 120mm fans per side, so it's on the upper end of what most use size wise.
Or for a much larger area core: Fedco #2-192 / GDI #399030 this is the largest heater core ever made so far as I've been able to find. Much larger cooling area than the above core, but will give higher water side flow resistence. I posted this one as I'm not sure how much you need, but this core is huge for most peeps uses. This core can take 4 x 120mm fans per side!
With a pump that large may I suggest you consider creation of a dual loop water rig. By spliting that pumps flow in half with one half going to the CPU block & the second half going to the GPU/NB you'd reduce your system resistence a great deal. Example
Monster pump=>dual parralel 2-342 cores=>
core "A" outlet => CPU block => single shared RES
core "B" outlet to GPU & NB blocks => single shared RES
Single RES =>pump inlet
A dual loop of this sort would have only approx. 30-35% of the resistence/headloss as compared to if you ran it all cores and blocks in series. Depending on the blocks you choose this dual loop might run anywhere from 3.5gpm to 4.5gpm. Sad fact is that pump is just plain driving more flow than even a dual looped water rig can well use.
Best of luck and I hope this helps.
