"The cake filled a growler, and after a week in the fridge has settled to about 2/3 yeast, 1/3 beer." That's 2/3 trub. The only way to know how much of it is yeast is to use a microscope. I wouldn't recommend just pitching in a new batch. Since you didn't wash it, it is going to have high amounts of non-yeast trub (proteins, lipids, et al). If you make a starter using some of your trub, once it has propagated; that is formed krausen and begun to settle, you can swish it, let it settle for 10 minutes, decant it into a sanitized container, let that settle until it is trub and beer, decant and pitch the slurry. That will avoid re-pitching some of the non-yeast trub. Ideally, you should do it with a large starter (at least 2 liters) since you will be ditching some of the trub.