Hi Guys, As you can see I'm new to the forum and I'm from the UK. As the title says, I'm about to purchase a new iMac 27" (not the 5k model). I've got a couple of questions I'm hoping you guys can help me with. 1) I'm wanting to have an external SSD using Thunderbolt to boot Mac OS off of - I've done a little bit of reading and I'm thinking of going for the Samsung 840 evo. Now there are two options on amazon UK - 840 256gb normal version or the PRO version for £23 more - what are the differences? Also how do I go about finding an enclosure to put this in that enables thunderbolt? The only one I have seen costs the same amount as the hard drive - there must be a cheaper / more viable option? 2) I'm wanting to add an additional 16gb ram (2x 8gb sticks) and keeping the standard 8gb inside - I've heard crucial are decent company to source these from. Are there issues with having different sized ram sticks in the machine? ie 2x 8gb and 2x 4gb? Appreciate your help guys. Gaz.