I'm very underwhelmed. LR4 was an improvement over LR3, but the subsequent improvements to LR4.4 have been to sort out bugs and add a few more cameras. In my view, this "upgrade" should really be called LR4.5. I would like a significant addition, like HDR, before I would upgrade. I hope that at least they have improved autotone which is largely unusuable and not nearly as good as that available in free products such as Microsoft Office Picture Manager and Picasa.
I find the speed of LR4 adequate.
I will wait for LR6.