I can't find any specifically comparing those two, but it'll be about 10-15W less at idle (which is what it would be downloading files). It's REALLY not worth it for the time and energy spent changing all the settings every night. I mean, if you were truly worried about saving such a small amount of power, I'd just download the files at some point when you're using the computer and unplug it at night. That's the only way to make a dent in power savings.
Power savings from a computer is honestly the last thing you should worry about, unless you pay $2.00 per kW/h. I run my PC 24/7 365 though, and my power is relatively cheap, but even if it wasn't, I wouldn't really care about trying to get pennies of power savings from it. Again, it's just not worth it.