I am currently using Lightroom 3 on a Mac Mini and considering whether to update to Lightroom 4. I am not much concerned about a slowdown in cataloging, importing or exporting but I am very concerned about processing/editing speed. I have a Mac Mini mid-2007 (2,1), 2GHz, Intel Core 2 Duo (64-bit) running on Lion 10.7.4. My RAM is maxed out at 3GB. Will I see any significant sluggishness if I update to Lightroom 4? If so, would a computer upgrade to a Mac Mini mid-2011 (5,1), Intel Core i5 (64-bit) with RAM maxed out at 16MB provide a significant improvement?