@Lazure. No, you can't just download the ISO and plug in the key because when you go to activate an OEM it tells you it's already installed on an existing machine. At least that's the message I got when I tried it, even after saying it was being re-installed on the same machine. And they actually blacked my serial key. I had to phone M$ Australia to get it sorted; and that was quite an experience.
And no, sluggish performance has not been an issue. I do acknowledge that excess RAM can potentially slow machines. But I like experimenting to find things out from hands on experience, related to the type of work I'm dong. Obviously hyper-threading is only helpful if the programs you're working with are compatible with it, etec, etec.
I don't have any formal qualification with PC technology, but I am a graduate Electronic Engineer, and just like tinkering. I guess I'm a bit Neanderthal in the sense that I usually read the instruction manual after everything else has failed. And I also admit that attitude can occasionally have dire consequences.
Anyhoo, the amount of RAM was incidental to the main point of my post in relation to Vista, which was to show that it is a very respectable, solid OS if installed on the right hardware, especially SATA3 SSD HD; good graphics and adequate RAM. And can be justifiably used as a flagship. My rule of thumb with RAM is that it's better to have too much than too little. And it's so cheap it doesn't matter.
Edit: Incidentally, the machine that has Vista on it was not custom built for Vista. I originally had Win7 Ult 64bit on it. When I upgraded Win7 to a high end machine, I put Vista on the old Win7 rig and never even thought about reducing the RAM. With Win8, I built an entirely new rig.