So long as you keep your nVidia drivers up to date, you will be fine. NVidia are 99% of the time really good at having their SLI profiles ready to go with a driver update close to, or before the release of a major game (AAA title type games), meaning you get SLI performance from day one.
You would be kidding yourself not to expect more noise with an additional GPU in your system... How much of a problem this is for you depends a bit on how sensitive you are to it. It becomes a bit of a balancing act with how high you run the clocks on your GPUs VS needing the fans to run on a high setting giving you more noise. You'll find as they go over a certain % speed they will really kick into gear giving you much more noise, but so long as your OC is moderate and you can keep them cool without having your fans run on too high a level... the noise shouldn't be too bad.
Microstuttering is a bit like the Multi GPU bogey man. There are those who claim to have seen it... you might even see a suspicious video on Youtube here and there that if you squint and blink at the right time you will see a microstutter... But seriously... it is conceivable that you might encounter it on the very rare occasion you purchase a poorly developed title, but it's not a factor I put into my basket of worries.
The h80 is cooling for your CPU. Those GPUs have their own AM cooling systems which will dump heat inside you case. This is where having a case with good fans really helps.
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