stepping down on yeast (round two)

That'll be quite a healthy and happy population of yeast for a considerably smaller beer. I would imagine it would ferment rather quickly. I've done this one time with a Belgian IPA to a Belgian Pale Ale and it was definitely noticeable as the fermentation on the second batch (belgian pale) was over in two days with the exclusion of some finishing up. I think my gravities were 1.065 to 1.048 (I'd have to check my notes). I didn't have any off flavors from such a quick and vigorous fermentation but you've got an entirely different yeast strain and two different styles of beer.

Edit: Love the Scottish Strain by the way. I fermented this years pumpkin ale with it and man does it bring out the maltiness in a great way. I'm considering throwing another (different) batch of pumpkin ale on top of it now - thanks for the idea.

 

You should be fine. What I usually do in this situation is save half of the cake in a mason jar for later...then pitch the smaller beer on the remaining cake.

 

If you are going lower on a subsequent beer, you will be able to reserve a significant portion of that yeast cake for another beer and no worries about underpitching.

My experience with the Wyeast 1728 is if you pitch onto a big cake, it will ferment very aggressively. Even if it will be a lower gravity re-pitch, be prepared for it to take off, get hot, blow hard through a blowoff tube, and all the rest.

 

Stone does it with their beers. All the beers that use the house yeast get a repitch from the IPA. But that is their yeast, not yours, so YMMV.