Tried the 756 front. Yanked it off and replaced it with a 773 front. Much better! Been running 773 rears for a while. I get pretty good life out them - probably about 30 all day rides per rear tire. Talked to the Dunlop tire mounter at the GNCC a couple of years ago. He recommended the 773 over the 756.
The 756 seemed to work well in wet sand, but was awful in deep dry sand. I suspect these characteristics are why MX'ers like the 756 - I can see where they'd be excellent on a groomed track.
Dunlop certainly isn't the only game in town. Michelin S12 is very popular down here. A few guys I ride with run a Dunlop 773 in the back and a Bridgestone M25 up front.