The best thermally performing GPU blocks are still the GPU only blocks like the D-Tek Fuzion GFX and Swiftech MCW-60.
The full coverage blocks trail by a few to several degrees, the simple difference is surface area contacting the water directly above the GPU. All of the GPU blocks are very simple and large channels.
There's no replacement for heat transfer surface area, and micropins are king baby!!
With that I like the D-Tek GFX for GPU only loops, the best performing GPU block there is that I know of. The Swiftech stealth also performs well, but the aluminum top gives me the alumageebee galvanic corrosion heebees...
The second best is the MCW-60 and it's better suited to multiple block loops than the Fuzion GFX because it's much lower pressure drop.
I suspect the Maze 5 performs somewhere between the MCW-60 and full coverage blocks in thermal performance. It's definately more surface area than a full coverage block, but it's not nearly the cooling power of the MCW-60 or Fuzion GFX.
Also full coverage blocks have that nasty habit of dumping all that memory heat into your loop. Probably on the order of 50 watts or more, this alone means your whole water loop is likely going to be 1-2 degrees warmer, so your CPU block gets another degree from that alone.
Full coverage blocks are popular because they look nice and you don't have to worry about keeping the ram airflow going. On an SLI setup, it's pretty hard to keep air flowing between all those blocks, so full coverage makes sense there.
In the end, it comes down to personal preference on alot of it. Some video cards are much more voltage limited than cooling limited, so arguing over a few or even 10 degrees is moot.
My 2c although I still like the GPU only block options..