I'd upgrade to an SSD and add 8 GB of RAM. I purchased a 15'' MBP and sold my 2008 iMac. I kinda miss my iMac now and I'd like a bigger screen. I managed to talk my wife into letting me get a Thunderbolt Display if I downgrade to a 13'', since it'll save $500. I wouldn't mind the screen size loss when traveling, but I'm worried about the loss of speed over the next 4 years. Is a 13'' MBP w/SSD + 8GB RAM fast enough to keep up with new OS updates and Aperture (the only heavy program I use) over the next 4 years? I'm just worried about lag and freezing. I'm also worried about lag on the Thunderbolt Display. I don't game on my Mac. Like i said, Aperture is where I notice my old iMac lag the most on ML and even on my 15'' MBP, which I haven't upgraded yet. What do you think? I either stick with my 15'' MBP or I go 13'' with a Thunderbolt Display.