? Install LR4 with LR3 / LR4 Beta on machine
Update: Installed LR4 and selected the LR3 catalogue as one to be updated.
Will leave LR3 on the hard drive until I'm sure everything is working as it should in LR4.
So far, LR4 seems to be slower than 3; but I'm very happy to be able to import and work with my D800's RAW files.