It won't work, SLI requires the exact same card (both would need to be either 1080 or the Ti version) and I wouldn't recommend going for SLI unless your gaming with a Ultra Widescreen monitor or 4K since the performance gain is minimal at lower resolutions.
As a side note you always do get a little bit of micro stuttering with any kind of SLI, best going with the best single GPU you can afford. I know when aftermarket/hybrid versions of the 1080 ti come out I'm selling my SLI setup and grabbing one.