Re: 2560x1440 not working..
Nope, I got the same resolution in OSX. Its actually also the same that I get with my old mDP->DVI adapter from Apple. I already returned the adapter and I'm now wait for the DP adapter.
BTW, a collegue successfully drives the display at full resolution via DP using a Lenovo T410 and a new docking station, so DP is working in general. Another collegue already bought the big new Apple adapter but this is my last option..