I always run the 64bit udk build because I have never had a reason to ever run the 32bit build before but today I accidently ran the 32bit bit build and it was running very very sluggish. So to make a long story short I found that d3d9 is throwing a warning and spamming it to the output window which is why its running so slow:
Direct3D9: (WARN): Device that was created without D3DCREATE_MULTITHREADED is being used by a thread other than the creation thread.
This problem does NOT happen with the 64bit version.
ATI Radeon HD 5700 - latest drivers.
Intel Core 2 Quad CPU Q8300