Full Copper vs Full Nickel

Solution
Both blocks are copper. Almost all blocks are, copper is simply much better then nickel for heat transfer. The "all nickel" block is only all nickel on the top; the actual block that does the cooling is still copper.
As for the chillers, it is going to depend on what they are made of. The actual tubes that the liquid comes in contact with.
Copper is usually the preferred choice for heat transfer in pc parts. That's the reason for copper bases on coolers, direct touch copper heatpipes, copper water blocks etc. Only a few air coolers are all copper mostly due to the sheer weight. They can still achieve decent cooling with copper in key areas and aluminum elsewhere (not in watercooling because of galvanic corrosion) to reduce weight but copper is a better heat conductor.
 


But it would be fine to use the full copper block if I'm not using any radiators to cool the system and relying only on 2 800W liquid chillers?
 
Both blocks are copper. Almost all blocks are, copper is simply much better then nickel for heat transfer. The "all nickel" block is only all nickel on the top; the actual block that does the cooling is still copper.
As for the chillers, it is going to depend on what they are made of. The actual tubes that the liquid comes in contact with.
 
Solution