iMovie 11 and quality of AVCHD-AIC-MOV file conversion?

If you're doing any editing in iMovie there's no way to skip that step of converting to AIC. That's what it uses to regenerate all the missing video frames that AVCHD 'estimates' in it's attempt to make much, much smaller, highly compressed file sizes. If you're not doing a lot of editing at all, but just want to create Blu-ray disks, skip iMovie altogether and maybe just try to come up with A Sony Vegas only solution? I guess I'm curious why you're going back and forth Mac/PC and Vegas/iMovie.

That's true you can build an incredibly fast PC and given the graphics cards available too I imagine Vegas can take advantage of them for rendering effects like transitions, and titles too. My feeling is the best you could hope to do (and it's going to eat up a ton of disk space) is to Import using Full Size and let iMovie do the conversion to AIC. Then for export, try the largest FullHD size available under the Share Menu > Export Movie... All the biggest sizes should be available when you go to export it.

Then from there, import it back to your PC and make the AVCHD DVD-R disk. I think that's going to keep the frame sizes big enough to take advantage of your Blu-ray playback device, and not touch the video frames too much in between. But files sizes are going to be incredibly large compared to the file sizes coming off of the AVCHD camera itself. So be prepared for some file size bloat.

No problem, I'm always trying to keep up with the newer cameras and formats. I have an older pre-Blu-ray/AVCHD version of Toast. So I haven't kept it up to date. Toast would allow you to stay on the Mac from importing into iMovie to final burning of the AVCHD DVD-R. That could save you a lot of time moving big files back and forth to the Windows computer. And that time saved may be worth the money. I say use your best judgement, everyone's situation is going to be unique.