To be fair, a lot of people exaggerate how much power they need. I have a 650W corsair in my PC, and its a great PSU, lovely stable rails, and stability certainly isnt an issue with my system, my system idles at a shade over 100watts, and I've never seen it draw more than 250 (since I upgraded to the ATi 5850)... The old 8800GTX used more power.
If you look at a budget mid range 650W powersupply like the OcUK Value PSU's and then consider them as 350W supply, and dont overwork it, the odds are it will be as stable, and reliable as a high end PSU pushed hard.
You can easily run an i7 (8 or 9 series) at stock speeds, a single GPU, an SSD and a hard disk, plus appropriate air cooling etc on a mid range 650W... And thats what these supplies are.. Mid range... They are a world better than the 400-600W PSU's that are thrown in free with many PC cases.