How many watts? 4670 vs. 4830

These 2 might fit in my budget, but I'm wondering how much current they will use. This is for a new system, at least 500W PSU, Q9400. Gaming would be pretty limited, mostly used for browsing the net and so forth. I'm wondering how the 2 cards would compare in power usage while idle. I understand that the 4830 probably uses 30 or 40 watts more while under load, but this would be for limited amounts of time so the power usage at idle is more important to me. (The computer sits at the end of the sofa so we don't want it to be like a leaf blower or a bathroom heater.)

Do n`t forget to read the whole review!
There are also a few passively cooled (no fan) cards out there in the wild but availability is patchy, so it depends on your location.