As you suggest the highest speed at which the shutter is at some point fully open will be faster than the quoted flash sync speed, to allow some variation in flash timing, probably just under a stop faster.

I don't have any information for the D7000, but the Canon 1D mkIII has sync speed of 1/250s with most flashes. When a Canon EX flash is used the camera can sync at 1/300s by improving the timing, according to Canon:

"For the X-sync contact, the mechanical contact has been eliminated to prevent contact scorching and wear. By employing PR signals for the electronic X-sync contact (a semiconductor switch), reliability is improved. By optimizing the sync timing, an X-sync speed of 1/300 sec. is now attained with EX series Speedlites. With non-EX Speedlites, the X-sync speed will be 1/250 sec., the same as the EOS-1D Mark II N's."

1/300s is not the limit however, by further tweaking the timing flash timing using a pocketwizard it's reportedly possible to get the 1D mkIII to sync at 1/500s (with barely noticeable letterboxing), according to Rob Galbraith:

"The EOS-1D Mark III, EOS-1D Mark II N and EOS-1D Mark II are the only camera models capable of a nearly-clean 1/500 using the first HyperSync mode, but all Canon cameras will see a one or two step increase in usable shutter sync speed compared to previous PocketWizard transmitters. The bump is greater still when compared to certain other wireless triggering devices."