HD4000 is very slow when rotated 90/270. OS is Windows XP. Using latest driver (5421, 7/27/2012).
Disabling acceleration (control panel -> display -> settings -> advanced -> troubleshoot) fixes the performance problem, but then DirectX apps don't run and the Intel control panel doesn't run.
Here's another funny thing. Performance greatly improves if a 2nd monitor is connected.
Again, this is only when rotated. When not rotated, performance is better (or at least not worse) with acceleration enabled, and adding 2nd monitor makes no difference.
Can you provide the following information please:
-How much memory do you have in your system?
-Is it a laptop or desktop?
-What CPU are you using?
-Is it Windows XP 32 or 64?
Additionally, can you go ahead and try running a movie/youtube video while having a single screen rotated, and tell me if you still experience the issue?