I recently filmed the new Nissan 370Z roadster. It was shot over two days and three separate locations with the Canon 7D.
On the first day the car was shot in Spanhoe airfield in Laxton. We filmed in an old aircraft hanger which was a great location to start with, but naturally a little dark.
Of course you will need a monitor for playback to see the noise. The small viewfinder on the back of the camera is not capable of showing detailed noise and so if it looks good on the back of the camera, it des not necessarily mean you won't find noise on the image when you get it back to the studio. There is nothing worse than getting it back and seeing that the image is not usable.
However, if you get the balanced settings correct in low level light then the image will look great with minimal lighting budget and costs.
The Second location was still in Laxton near to a fantastic viaduct, which gave us some great images.
On the second day we filmed in Chobham near to a National trust reserve and just off the motorway. It was a great location, but again I noticed a fair bit of the 'jelly' effect that the HDLSRs are known for.
The roads where not perfectly smooth and so whenever the car bounced over a bump, it then had an exaggerated effect on the camera.
I don't feel like I would be confident to direct a film on the Canon that entailed a lot of motion or traversing of the camera. I could happily live with the noise issue and just add some extra lighting to counter it...but the jelly effect is something I don't think I could ever get use to.