- For best moon pics, you would need much more focal lenght than 400mm eqiv
Yes, in all fairness, the longest lens you can get is the best for the moon - unless it's just going to be part of the frame. I've shot the moon with the 40D and a 1000mm telescope. The telescope came with an M42 mount which replaces the eyepiece, so a simple M42 to EOS adapter was the final piece of the jigsaw.
However, even with a 1600mm equivalent focal length, it still took a bit of cropping to get it tight. A 1.4x TC might have done the job. There were no end of issues though - street lights, the moon racing across the frame (a fast shutter speed is a must), and the equatorial mount wobbling all over the place when walking nearby. I found tethered shooting through the USB cable from the laptop with EOS utility to be about the best - it allowed me to avoid shaking the setup and get the focus right at 100% on a big screen. And then I was left with horrendous CA, but it was nothing that only using the green channel and turning it into a B&W image can't fix.
Either stick with the TC option as while it's compromised for shooting the moon, it gives you plenty of other genuine shooting options, use a telescope (if you know someone with one, even better), or to get the best optical quality, simply buy that 1200/5.6 that's appeared on ebay.