The ACX failed to impress me. Even Asus' DC2 was just OK.
Reference cards are too loud IMO and can't match the temps of a real cooler.
Check out Techpowerup's review of the MSI Gaming w/ the Twin Frozr 4 cooler. The fans are 100mm. AFAIK, the ACX is 90mm? I can confirm that it is without a doubt in another league when it comes to cooling prowess and acoustical footprint. The sonics produced on this card are fantastic and I'm VERY particular when it comes to the way a fan sounds. The ACX's fans produced a whine that drove me nuts. The DC2 was not annoying, but still louder than I'd like.
Here's a video showing the difference between Asus' DC2 Cooltech fans and the MSI's TF4 Propeller fans. Yes, the Cooltechs do exhaust a bit of air out the back, but honestly as long as you have a good case, this should not be an issue. I have a single rear exhaust that's a 120 and spins @ 1500 RPM. That's enough for my 4670K @ 4.2 Ghz and 1.3V AND the MSI 780 Ti TF4 @ 1210/7800 spitting all kinda air into that case. I see no reason why anyone would go reference.
What does the fan speed max @? Also, what size are those fans? They look like 80's.
I've used both PX and AB. The only differences I noticed on my Ti are:
-PX is ugly
-PX's GUI is the opposite of efficiency
-PX has problems w/ detecting correct clocks and total memory usage
IMO, AB is far better and updated WAY more often.