Can't decide on which HD option to choose. Base 500GB, 750GB or 1TB? I already have an external LaCie 500GB Big Disk Extreme and is half empty and I've got about 25% space left in my iMac (250GB) 1) Will the 1TB add extra heat? 2) Should I do a DIY to the 750GB/1TB? But I don't see any 1TB SATA drives right now. 3) Is Apple offering a good deal on these HD options? +$150 for 750GB or +$450 for the 1TB I'm concerned about the heat from a 1TB HD inside such a small enclosure and the value of the options, whether a DIY is a better option.