So I've been using Aperture again since I got a newer mac, the latest that will run on Snow Leopard. So I get the itch to try LR4 on the MacBook that I have. What I found was that LR4 actually ran faster on my macbook then Aperture 3 did. LR4 also ran faster on my Macbook with Intel C2D with 2.5 GBs of RAM than a Sony Viao with Intel Core 2 Duo and 4 GBs of RAM. So it looks like I will be still work LR4. Macbook specs are in my signature.