MTI's Kahlo 2 might meet our needs for the master bathrom's bathtub:

66" length, 36" width, 19.5" total height...not too big in any dimension, and possibly not too tall to easily step into as well (we're pondering whether we'll need a step for the tub or not). We hope to visit local showrooms with tubs of comparable size to truly test the soaking depth and step-in height.