What do you plan on using it for? ....list the top 3 things.
What are you coming from?
You likely know I'm a huge Canon fan and own a 1D series (older MKII), a 5DMKII and a 40D.
I've looked and handled both the above and will say they are great units. Seeing as your needs are for real estate purposes you will definitely enjoy working with them. That said, I will advise while both have video capabilities, I wouldn't count on even the MKIII replacing a dedicated video camera for all around use.
The MKIII 1080p and the new processing engine helps the shutter roll issues that at least I notice on the MKII, but they are still there. The key is to pan slowly and if you shoot sports, shoot from the corners were zooming trumps panning. Your limited to mono sound and it does tend to pick up IS movement within lenses. I won't beat a dead horse, should work fine for filming homes, where music or no sound may be used.
We could talk about the 1Dx all day, but unless you're shooting sports professionally, you probably could better spend the $3,500 difference in price on glass.
If could justify the purchase, I'd jump on the 5DMKIII.