I was looking into the "big Dow" and IMO you're better off trading 2 YM contracts.
The volume isn't there for big dow, take a look at this:
$10 Volume
http://www.cbot.com/cbot/pub/page/0,3181,978,00.html
$5 Volume
http://www.cbot.com/cbot/pub/page/0,3181,1632,00.html
Plus the margin...