Moon (not) over Miami

Any suggestions for getting a sharper moon? My camera shop told me to switch off image stabilization on my lens, since the camera was mounted on a tripod (did that...). I'd read someplace that good moon settings are shutter at 1/125, f/8, ISO 100. My moons were too dark for that. I messed around with the ISO settings as you can see below. Except for a little tweak to exposure and brightness in ACR, and cropping, these are pretty much straight from the camera.

(Above) Tripod mount, self-timer, ISO 100, shutter 1/40, f/6.3, focal length 270mm

(Above) Tripod mount, self-timer, ISO 400, shutter 1/125, f/6.3, focal length 270mm. This shot was about 10 minutes later than the first one; the orange was quickly fading.