HDV Greenscreen

OK - Maybe I've missed this because this seems like it would be a basic question but I'm not finding much information about shooting greenscreen with HDV cameras. Let me preface this by saying that I realize that HDV is NOT the best format for shooting green/blue screen but going true HD at this point is probably not an option.

I would think that the better the resolution, the better the key would be but even that does not seem to be clear cut. The Canon xl-h1 would be great but you can only get the highest resolution by bypassing the on board tape and going straight to an external source. The Panasonic HVX theoretically should be good (with true HD to the P2 cards and 4:2:2 color space,) but I've heard of problems with a "halo" around the subject when keyed. I've also been looking at the Sony z7u but I can't seem to find the resolution when recording to the CF card.

Can anyone make sense of this or point me in the right direction for more info?

Thanks!

Elisheba