I'll soon be getting a new iMac. My ext. backup is a LaCie quadra, via Time Machine. The port on the iMac is USB 3. Should I use a USB cable to connect the two? I'm wondering if the bottleneck would be the spinning disk, or data rate of the cabling. It would be USB 3 > USB 2. Or should I spend $$$ to get a USB 3 > eSata adapter?