I acquired a used 5D MKII from an eBay seller a while back and am considering Magic Lantern. The software adds a lot of functionality. One of the changes after the upgrade is the MKII can write to 64GB CF cards. For long shoots, this would be useful.
All CF cards are pricier than SD cards, so if you're serious about DSLR vide, you'd probably want a solid high speed card. They do come with a big prize tag.
Here's the Magic Lantern site: http://magiclantern.wikia.com/wiki/Magic_Lantern_Firmware_Wiki
The eBay purchase was $1200. Not bad for a camera that still sells for more than $1800 used. It does have 183,000 shutter activations, but I'm using it to get comfortable with DSLR video.
