Like (I suspect, many) folks, I am experiencing redraw lag in LR4, so I don't immediately see the changes to the image when I drag the development sliders. Here's the hardware I'm running:
AMD Athon II X64 620 2.6gHz quad core
8 MB DDR2 memory
Radeon HD 6670 w 1GB memory
Dell 27" 2711 monitor, something x 1440 resolution.
Lag was awful with my old Radeon 5450 card, so I upgraded to the 6670.
It looks like in order to get real time changes to the image sized to fill the develop module window when I make exposure etc. adjustments, I have to reduce the display size of the image down to 1:4. Sized to fit the working window, I am experienceing lags of .5 to 1 second.
So I have a couple of questions and a comment. How fast a graphics card would I have to move to get rid of the lag? Would more system memory or graphics card memory make a difference? Would it make a difference if I had LR on a dedicated install with nothing but the OS, LR and Photoshop installed (I have a fair amount of software installed on my box)?
And here's the comment. If I open the same DNG in the 2012 process version of ACR and perform the same operations, with the image the same size if it fills the develop window in LR there is zero lag. None. So what gives with that? (So I may end up just going back to developing in ACR in the end.)