I'm thinking of upgrading a few bits of my iMac, which is one of the previous models (still unibody, but the glass doesn't go all the way across the front). First of all, SSD. How much speed difference should I expect, and are there any SSDs that anyone can recommend? I'm looking for either 250gb or 320gb. Also, and most importantly, how hard are they to install? If the process is too tricky I think I may pass. Secondly, RAM. I upgraded my RAM when I first got my iMac from one to four GB, but I think I may have got some pretty slow stuff as I went for the cheap option and got it off Amazon. Is 667mhz the fastest RAM that my iMac can take? Thanks.