Any advice gratefully received on a purchase decision. Planning to replace my ancient (pre-2010 I think) MBA with a new 11". Will be used for very large presentations with multiple embedded videos (worse still - PowerPoint!). Current MBA freezes on occasion so time to move on I think. So here's the question - what do I upgrade? Processor, RAM or SSD? Can afford (at a push) two out of three. Want the 11" as will be used mostly when travelling and size/weight are important. Thanks in advance for any thoughts.