Looking to replace my wife's mid 2009 MBP 13" with either a MBA 1.7GHz i7 or MBPr 2.4GHz i5, both 13" models with 8GB ram and 256 SSD. The main reason is that it's just too heavy for her to be carrying around in her purse. The most important features to her are weight and performance. Whether or not it's a retina display is not the primary concern. As far as performance is concerned, is there any noticeable difference between the MBA and MBPr when running Parallels?