I use my old 500gb drive to store all temporary stuff (windows temp folder, adobe scratch disks etc), and anything that needs thousands of small files to avoid unnecessarily fragmenting my C drive. However, it has started slowing down a lot recently (28000 hours of use so maybe it's dying, last year I moved the pagefile back to C as the read/write wait was slowing the entire computer), plus an upgrade would be nice, so I was thinking about getting a 4TB drive for temp files and games.
The only reasonably priced 7200rpm one I found is a Toshiba USB 3.0 external drive, so I'm wondering if USB 3 is sufficient for use such as what I mentioned above? The current 1TB external I have is a bit unreliable and slow, (good for storing media but not much else), so I don't want to risk it without checking first.
Update:
I have the drive, it's read/write speeds are over 50% higher than every other drive I have, and in its current new state, it can write lots of small files faster than my existing drives can. This is also using the PCI to USB 3 extension, not the slots built into the motherboard. I'll update this if anything changes, but the answer to the question is there definitely doesn't appear to be any loss in performance.
Update 2 (1 year later):
I'm using it with an SSD for the C drive now, and there have been no problems for at least as long as I've had Windows 10. I'm using it to store around 2.3TB of games, photos, and music, and it's still going fast. Maybe you might not get the same experience, but I'd say it's definitely worth it for saving money.
Best Answer
USB 3.0 has an upper limit around 5.0Gbps. SATA III has an upper limit of 6.0Gbps. Regardless of overhead these rates are far higher than what a mechanical HDD can sustain for large transfers.
Most mechanical HDDs won't be able to sustain more than about 1.5Gbps (HDD Speed results). So I doubt you would notice much difference in performance. Real world performance would be affected more by the HDD, chipset and drivers (be sure to keep your drivers up to date).
Just remember to treat your external HDDS gently. Don't knock them while they're running, this could damage the platters. I still tend to eject my usb disks that I use for backups just to be sure they stay reliable.