It's interesting to note, on my 26" monitor the slow downs eventually happen, just takes a bit longer. It seems that the longer I have LR up, with D800 files, the slower it gets, which to me points to a memory leak. If I reduce the window size it helps a bit for a while, then slows down again.
Same machine Capture one runs insanely fast. So, I find myself working over there more often.
I am going to try LR4.3 on my Macbookpro over the weekend, 4 core, 4 threads, 16GB of ram, it's the last gen before the retina display ones.
Thanks for the ideas and pointers.