I think the mention Micro Drive not CF cards lah. Basically, I think the Live view mode consume more power and so does the micro drives. Therefore combining both will drain away your battery faster. just my thought.
And for the record, in case you all had not discovered it yet. Have you all tried using 2 extender? I did a test but due to leagal reason, I cant post the photo. I mounted my 500mm f4.5 (non IS) lens on my tripod, add my 1.4x TC and 2X TC. manual focus on a $10 bill about 25Meters away using the 10x magnification on the live view. using a cable release, I waited for the image to stablise (heehee no need IS lens liao) and release the shutter.
At 100% crop I can see the lines on the President's face clearly without any sharpening at all. Try that out Guys. 40D rocks. Now I dont need to invest on longer lens.