Ask any professional poster, this far out head to head match ups are near useless, but what is a little more telling is:
A's approval/disapproval vs. B's approval/disapproval...the polls always converge on that anyway.
Totally concur, but what's interesting about this election cycle is that everyone has net negative approval ratings: Congress, Congressional Republicans, Congressional Democrats, Obama, and the Republican Presidential candidates.
Admittedly, head-to-heads are a lousy way of augmenting this information.