For whatever reason, I perceive the SP10 in a different way than the BK9. Maybe thats why its not brought up as much?
So here is how I think of them: (And to be clear, I own a BK9 but not the SP10, so I may be biased.)
The SP10 is shaped like a fighting knife (huge clip point, big extended guards top and bottom, etc) but is built like a chopping knife (very thick, lowish saber grind, etc). Because of those things, I think of the SP10 seems somewhat conflicted in its design ethos. I guess I for some reason expect it to be either thinner (more like a giant USMC) or have a more useful clip point or a drop point (to make it have more mass out front for even better chopping). The way it is right now it would seem like the guards (and the ricasso) would get in the way of small tasks, and you'd more or less use it like a hatchet. I'm sure it chops pretty well with that thick blade and lowish grind.
The BK9 seems to make more sense to me. The clip point is still there, but it is far less exaggerated (its a much smaller straight clip, which should increase the strength of the tip relative to what it would be with a bigger clip). There is no top guard, and the handle design works like a bottom guard, so I can still get up close and do good small work with it. Its thick enough to withstand anything I can think of doing, and has a pretty high saber grind, so it is still pretty slicey for a big knife. Not to mention its actually fairly light for a large knife.
The SP10 is no doubt a good knife, and for large rough use I'll still continue to recommend that people check it out (chopping/batoning/digging), I just for some reason think that the design of the BK9 will help it be a better all around tool.
TLDR:
BK9 feels very well designed and balanced, SP10 seems to have some design elements that are at odds with itself.
For some reason I think of the BK9 as competing with the RTAK II much more than the SP10. Just my two cents.
And Jeepster, I've been curious. Why do you call the BK9 a "Lego" knife?
*Just to be clear, I'm not attacking anyone, or any company. I'm just saying how I think of them when I look at them, and some of the reasoning behind why I think that way.