780 Classified once in tri sli are a bit too tight: that's what I found this morning.
I checked the other two acx coolers and there is at least one blade for fan that goes over the limit (risking to touch the pcb below).
Looking better they are pretty thin in the edge, maybe they got deformed by heat and air resistance.
 
 

3 ACX Classified in SLI. That must be huge amount of heat.
I swear with one Classified and fan speed on 75% I have over 15C temp difference if I remove side panel.
When I put hand near card air is not so much hot at all, warm only but still after some time temp increase on 85C.
I will build some cheaper version of cooler water-cooling with Swiftech H220X and if that is not enough I would put MCR140-X drive only for graphic. But that's solution for guys with one card if they don't want noise and no 500$ for water-cooling but still want better than AIO solution and full cover block and to replace liquid. If MCR-140-X is on front panel near card could be connected with rotary fitting and look amazing or EK Solid Tubing. 
I don't know how people use even 2 cards in SLI because ventilation in my case is excellent. 
Maybe is and blower style good idea but definitely not only blower style. Do you remember before how many people complain on noise with GTX580 Classified on 80-90% speed and GTX680 Classified. From other side GTX780/GTX780Ti Classified on 80% speed you hear only AIR.

Yeah, to make them work I put a silverstone AP182 on them but core clock still did throttle.
I'd like to see how evga will manage RMA, I mean: even the other two cards' fans are starting to deform, looks like ACX isn't working on tight sli rigs (tri, four).
I should move to watercooling but just for the waterblocks I'll need 300 bucks 

I just RMA"d a 780ti Classy for that very reason... Blade broke off too.... I have a 2 card SLI with good spacing. I'm surprised how different the cards were. The one I RMA"d ran on the warm side, upper 70s c,  and the other runs much cooler, low 60s c, and even out performed the warmer one while folding. I feel your pain!!!

Sure!
I'm using an Asus z87-WS (gives a stable 3-4 way sli), all stuffed into a Corsair Carbide Air 540 with a side panel mod that uses a silverstone ap182 to blow fresh air on the cards.