I think all have valid points based on our own experiences, outcomes and training. In a situation like this, it is hard to develop a formalized opinion on what method I would choose, as I do not have a live patient in front of me to help me decide based on the numerous observations that can be made of a patient. Personally, I would probably go for the IO as it is quicker and in my experience (although limited) more reliable. I would want access ASAP to give fluids and medication if necessary.
On the topic of c-spine precaution, if the patient has a high cervical fracture then movement could end life. So as Dwayne put it, Life over Limb and by maintaining a neutral alignment on the c-spine, I could very well be preserving life.
Just my $.02 for what it's worth