@Parappaman: The Arctic Fusion 550R uses a PWM controlled 80 mm fan, which several reviews say is nicely quiet. I think I'm going for the Artic, since I can find it at a fair price, and it's a Seasonic OEM like the Corsair VX and other well-reputed PSUs.
But I worry about the 80 mm fan. If it used a 120 mm fan I would have better chances of installing a more silent fan, while still pushing a fair amount of air for cooling. If the stock Arctic fan is too noisy for my tastes, then it will be harder to find a truly silent 80 mm fan I think.
This would be a argument in favor of the BeQuiet! PSU's, they use 120 mm fans, so I think they have better modding potential. I'd like to avoid modding if possible, but it could be a way out if I find the noise unacceptable.
This HTPC will be standing in a open bookshelf about 1.5 m from my sofa, where I'm sitting during movie watching. I'm trying to get it really quiet.

I'd really like the Seasonic X-650, but I can't find any local shops who have it.
So I guess I'm asking "how silent is the Artic 550R really"? I know it's hard to quantify; is it fx audible from 1 meter away with the case cover off? Compared to the BeQuiet! models, how is it?