If you want a lightweight fighting/tactical weapon that can do some light breaching duty the VTAC is the overall winner.
If you want a badass tool that is capable of crash/rescue or medium/heavy breaching then the K5 is the winner. But I can assure you it's a brute.
I think that as a fighting hawk the K5 will weigh most people down. I find myselff wanting to use two hands with it. But the K5 will suffer more abuse than the polymer handled vtac. They're both the best, just in different categories.
It sounds from your last post that a vtac will suit you better, so I'd advise looking at Haysknivesmontana.com for some comparison ideas. Their G41 is made of 0-1, and is the tool I'd buy if I were looking for a killer polymer handled tomahawk for everyday cary.
But wait, there's more!!!
If you wait a little while, Eddie is supposedly coming out with a lighter weight version of the K5. That may just be the lightweight/heavy duty hawk with the least compromises. Eddie???