I was going to reply this morning but instead I've been trying a little test all day.
My machine runs two 512 sticks of HyperX PC3500 at 2,3,3,6, another of my machines runs one 512 stick of Samsung PC2700 at 2.5,4,4,8. Rest of machine is A7N8X Deluxe rev 2.0, 2500+ o/c'd to 3200+
Just so I didn't stick my foot in my mouth I stuck the Sammy stick in dual channel with one of the Kingston sticks at 2.5,4,4,8 and all works fine. Mem slowed down just a hair according to Sandra (about 50). It may not be optimal, but it does work with no problems.
Mark