There is no 1 bike that is great for all things. The cyclocross bike is pretty close, but you'd still want to switch out the tires when going on the road--at least for any distance. Same for the speedbike off road. I suppose you'll have to decide which you'll do the most.
I must say, off road will not be too comfortable with a rigid fork. Pre 90ish, no mtb had a shock. Now they all do. But if you're just talking about dirt roads and trails, no jumps, then either bike would work.
I guess one additional difference with cyclocross bikes is that the wheels are usually beefier, with 32 spokes minimum per wheel. Some of the speed bikes (like road bikes) have lower spoke count because lots of spokes are not necessary when riding on roads. You might want to stick with 32 spoke rims. Doesn't narrow down the choices much though!
Take a look at the Cannondale Bad Boy. For more $$, the Bad Boy Ultra has a front shock but it can be "turned off" for riding the street. That might be a good way to go, but it's bucks!