I brewed a Strong Scotch ale 4 weeks ago, I pitched Wyeast 1728 Scottish Ale yeast that had been washed from an 80 schilling. I had 100 ml of slurry that I pitched, it was very healthy it had quit fermenting about three days earlier and been washed the day before pitching. My Strong Scotch Ale came out to 3 gallons at 1.087 and I shook vigorously for about 2 minutes to ensure there was oxygen in the wort. My mash was at 148, I fermented at 60 degrees, and the yeast has an average attenuation of 71% (I know this figure isn't perfect). Tonight I transferred the beer to secondary and the gravity is at 1.029, that is 64.8% apparent attenuation. My fermentation may have been a little cool for a beer of the gravity or I may not have gotten enough oxygen into the wort, maybe something else went wrong. Anyhow, I'm sure this needs to ferment more and I am considering pitching champagne yeast. My question is will champagne yeast take hold in a beer of this alcoholic strength or is it too late to pitch another yeast. Another option is that I have WLP001 American Ale yeast that I could make a started of and add at high krausen. Will champagne yeast work at this point, should I make a starter with champagne yeast, or should I use american ale yeast?
On another note, the beer is super smooth, you can sense an alcoholic presence but it is not hot or abrasive at all. Fermenting a big beer on the cool side is definitely worth the trouble. Thanks for the help.