Hey jamexr, I don't have a 1080 ti SC Black yet (Step-up queue), but I have recently owned two 970 SSC ACX cards in sli. But I haven't owned a blower style card since XFX made GTX cards . But I can share my experience.
 
The ACX and ICX style coolers are very similar to each other in how the handle airflow. They pull air into the fans, and out the sides and back into the case. While the FE cards pull air into the fan, and then immediately exhaust the air out the back of the case.
 
It is true that FE/blower cards are better for sli, as you don't have to worry about insufficient airflow in your case to cool them. They will run slightly hotter in general, but that's what they were simply designed to do, so you shouldn't really need to worry about 'hotter temps' (If you have decent airflow).
 
When I installed my second 970 ssc, I found that the top card would run 10 degrees hotter under load (Hottest I'd ever seen it go). All of a sudden the computer was outputting some serious heat into the case, as I didn't have blower styled cards. My cpu temp also rose along with everything else, so I had to look into how to improve the airflow.
 
Things to try:
#1: Check airflow: Do you have enough fans pushing air towards the cards? The cards temps should drop a bit if you have colder air going in.
 
#2: Lower the fan curve: All fans have a 'cut off' point, where after they reach a certain speed, they immediately become loud. My 970's were silent up to 20%, but at 25% they were audible, and past that they were like a jet engine. My current 1080 FTW is silent up to 40% fan speed, past that it's only slightly audible. Try to find at what levels work best with your FE cards, and try to stay under those speeds if you can.
+ Another thing to remember, is that if you do get ICX fans, that doesn't automatically mean your whole pc will become quiet, as you'll then have to get more fans to supply good airflow.
 
#3: Try a different PC case with side mounted fan: I own a Coolermaster HAF case, which has a fan on the side, positioned directly at the gpus. I would never use ICX sli in a case that didn't have that. I set the side case fan to pull the hot air out from the cards, and it was amazing! I finally had good temps, but my 970's themselves were still loud. For you though, you could set the fan to intake, and see how much that improves your temps. (I'd also imagine that the 1080ti SC Black will be quieter than my 970's, but you'd still need more case fans, which would defeat the purpose of getting ICX cards for a quieter pc...)
 
TLDR: Getting enough airflow in a case for ACX/ICX cards can prove to be a real challenge, which might require a new case to do so and more loud fans, but they should run slightly colder than the FE blower cards. Or get the hybrid kits if you want the simpler option for a completely silent and cool pc.
 
This post turned out to be longer than I thought it would... Hope this helps! (Also pics of my sli airflow experimentation... Also I used two power supplies for two months...)

The side fan: while not looking too appealing, works wonders for sli of both blower (Intake) and ACX/ICX cards! (Outtake)