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Sorry I've been of little help (well no help at all really!).
That is an odd problem - I've not come across it before.
From your description it appears both your Acer and HDD are happy to work at 3.0 but not together. Like you, I don't understand it. If I should have a brainwave, I'll post back.
In the mean time, I hope you manage to find a resolution.
Microsoft support actually had a great idea - to try the drive under Safe Mode, and then to try a Clean Boot. I am giving those a shot tomorrow morning, and I'll also try to boot into a Ubuntu Live USB to try it through there - hopefully there will be a compatible USB 3.0 driver available for Ubuntu.
Safe mode = same deal
Clean boot = same deal
and, incredibly... Ubuntu 13.10 Live USB environment = same deal!!! The 3.0 USB controller is recognized and active, yet when I plug in this WD drive it is rerouted to the USB 2.0 hub, actually the same hub that runs the USB 2.0 port right next to it. At this point I'm going to Acer support because this is an incompatibility that they need to address. I went to Renesas but they said that they don't provide end user support and that I should go to Acer.
Well, if there are no other ideas... looks like I am going to pay for out-of-warranty Acer support. Thankfully my SquareTrade warranty will reimburse me for it. I bet they're going to make me reinstall Windows even though I've replicated the issue under a totally different OS.
Update: I ended up trying one last thing before going to Acer for support. I thought that perhaps not enough power was being supplied by my USB 3.0 port to the drive, forcing it to "downshift" to 2.0. So I bought a Y-cable for $5 to provide auxiliary power from the adjacent 2.0 port. Result: IT WORKS. Immediately connected as a USB 3.0 device and transfer speeds are USB 3.0.
Solved. Kinda disappointed in Acer/Intel for the sub-par USB 3.0 port, though.
Note that the USB 3.0 specification provides the option of two power variants, 150mA and 900mA. Off hand, I don't know which is specified on the Aspire 5755 so you may be being a little unkind to Acer!
I think it's pretty clear that they used the lower power spec on the 5755. I'm not saying they are violating the USB 3.0 standard, I'm just disappointed that they chose to skimp on that (while not really informing anyone - yep you cannot find this spec from anyone and I only figured this whole thing out by accident).
Yes, I hear what you are saying. I am not taking sides here. I'm simply saying that, if Acer elected to use the low power option then so be it. I do agree with you re the stated spec - or lack of it. I too have found it very frustrating on occasion trying to get the 'real' spec of a product. Today's consumers are far more 'savvy' than of old and many have a real and valid need for the nitty gritty. Hopefully things will improve. At least you have found a work around!