I've never heard of the Oben before. However, I have a 679B and I use it frequently with a 400/f2.8 and TC-20eIII, so I'm pretty confident that it'll handle the Tamron 70-200 at a quarter of the focal length and a fifth of the weight. Actually I've been kind of looking for an excuse to upgrade the monopod, and I haven't been able to produce one...
I'm not sure about the head - I use a Markins M20. But while the 234RC is definitely not big enough for the Big Guns, I'd be VERY surprised if it gives trouble with a 70-200.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!