[V12|V12]

I must say, nice case man! Now on to what I've noticed:

1)Negative pressure IS better. Through experience, I've got 1x80, 3x92, 1x120mm and trying diff setups between them, I've found that my lowest overall case temps work best with the 2x92's exhausting, 1x92 intake and 1x80 exhausting...

2) If you could; my 120mm had a triangular shroud where the fan is on the bottom of the inner portion of the case, Pulling air through my HC from outside and directly exhausting it out to bottom of the case, as to avoid adding MORE heat to the case.
What you must understand is that CASE temp DIRECTLY effects water cooling temps, not as much as air, but think about it; Your HC is directly inside a box. The hotter the inside of the box, the LESS efficient your HC will be and the more temp load it will face. If you keep your case cooler, then it aids in the cooling with the load the HC has to tackle.

3) 25mm fans just don't produce enough pressure, pos or neg for me. I've got a 38mm and a monstrous 50mm and they both move more air per blade revolution, just based on common sense, thicker = more air moved by thick blades. They don't have to work as hard either to move more air. And they are usually quieter since there's more Tube for the air flow to be smoothed (Tube-Axial/Vane fans).
*** Try this, becareful though*** Take your fan & put something against it to partially block the air from exhausting, now take your hand and put it near the intake you'll notice that you actually feel some air blowing BACK out the intake from all the exhaust blockage... Now do the opposite, partially block the intake and put your hand near the exhaust... notice some air comes out... Now if you run a negative exhaust setup the extra neg pressure will aid in helping the HC fan pull in more air. Now if you make a shroud like I did, and if nothing's blocking the exhaust, the air has NO WHERE to go but through the HC--> fan intake and out the exhaust... Blowing though, the air can escape between the small space between the blades and the fan's frame.
*One more thing, when you try (if you do lol) the 1st pressure test, you'll notice the noise level is SIGNIFICANTLY increased, where as the 2nd scenario the noise level is much lower.... based on my experience/experiments Neg pressure is better, most PC fans aren't designed for high pressure loads...

Luckily the depot I live near carries nothing but INDUSTRIAL grade cooling fans (All metal frames, Thick magent/wire gauge saturators, some all metal construction!) fans designed for horrid temps and working environment. Comair/Rotron, Nidec Torins/Boxers, Papst Boxers are all some SUPER grade fans. If you get them new they are pretty pricey... used, I got a Rotron 120x38mm Whisper XL (new $43) for $5! Good luck with your cooling adventure!