You did a good job with it...got the right exposure for the flash that lighted the cat, and the right combination of ISO, shutter speed, and aperture to make the background lights a nice, bright color, not too bright and pale, not too dark and weak! I know whatcha' mean about getting a cat to pose...they're pretty much totally independent contractors... As you found, the combo of f/2.8 at 1/40 second and ISO 800 is a pretty good starting point for this type of flash + Christmas-season lights. The wide aperture of f/2.8 makes the "bokeh balls" big and round, especially with longer focal lengths like 70mm.