What version of Media Composer are you using? I don’t see a reason to use MetaFuze in this scenario. With v5, you can use AMA to directly access the 5D and 7D footage as well as the XDCAM. For I would create a base 25p project for your final sequence, but create 720p/50 projects for the slomo.
Once the 720p/50 stuff has been linked to, open those bins in your 25p project. Frame rate mix and match will kick in automatically so when you edit material intended for slomo, you need need to go to the effect parameters for each shot and set the rate to be 1:1 rather than adjusted. This will play it back as slomo, or even slower if you set the rate slower.
Once you get to close to your final, or final locked sequence, transcode the entire sequence to an Avid DNxHD format to easily prepare you for whatever output you need to provide for delivery.
You have quick start AMA guides for all the formats you are using here:
https://www.avid.com/US/products/Avid-Media-Access
If you don’t have v5, you can always get a free 30 day trial from avid.com as well. That will easily cover your 24 hours… 🙂
Michael
Michael Phillips