A powered hub only increases the max current draw, which is essential if power is an issue. The 5 items in the linked article boil down to that single fact. As far as I am aware it makes no difference to data rates because all the end user's data still go down the single cable back to the PC, powered or not. The data rates probably depend more on what types of devices you connect to a hub. A mouse and keyboard for example are interrupt devices that are not usually used at the same time so would not interfere at all. If you were streaming video and sending data to a printer, they could potentially interfere. The maximum data rate is not really affected, just the ability of devices to get their business done. If you are continually using your graphics tablet while trying to watch a video streaming via the same hub, that may not work too well either.
As data rates go up, conflicts should decrease. That is, until developers realize they can stuff even more data down the wire to their devices and back to square one. Ditto for making USB power available. USB 3 power is much greater than USB 2 so manufacturers now try to have "self-powered" devices.
As I commented on another thread, one often forgotten aspect is that a powered hub needs yet another DC converter to go along with the one for your printer, modem, USB HDD, kitchen sink. Also another wire to join the rat's nest.
Edit: Forgot to read the first post! If those are USB-powered
HDDs, then you would certainly need extra power if all are running simultaneously. Powered from 120V/DC converters, not. If all drives are trying to communicate at the same time, there will be a data bottleneck at the hub-to-PC connection whatever configuration. The laptop temperature may not have anything to do with the USB. Easy to measure, check MB temp with and without USB HDDs connected.
Edited by Nanobyte, 18 November 2012 - 11:48 PM.