Any question answered...

the ATAC is also a MTB pedal. Since I mostly do longer rides and not coffeeshop runs, I thought the SL would also transfer more power to the pedals. I also ride a road bike but currently with the normal SPD's. Nice for walking but perhaps not the best thing for riding (I find the play annoying)? That's why I wanted to know if the SL's can dismount when skidding.

Time ATAC man, SPD-SL can unclip and has for a couple of people I've known, longer rides are fine in time ATACs. If you're going for road pedals imo keos are far nicer than SPD-SL.

With SPD-SL pedals set to maximum tension you're clipped in, particularly with "no flow" cleats. Never say never, but I can't possibly imagine you would unclip during skidding, it certainly hasn't happened to me. In short, with SPD-SL you're clipped in.

Can't recommend the no float for skidding myself, I used the 5 degree and they were ok but at the end of the day I'm much happier with my keos.