Hi, I just installed PB4 on my late 2010 MacAir. It's a 4Gb machine and I can't believe the difference from Mavericks. I wear bi-focals for vision. They cover 'close-up' and 'far-away'. Until PB4 I always had to wear them when working on the MacAir. Now, I don't. The screen just seems so much easier to read. Whatever Apple did with the GPU software seems to have made things better. On the actual speed side of things it seems to be performing somewhat faster. Time will tell but just not having to wear the glasses is awesome.