If your budget can handle it http://rackstuds.com/ are great. about $60 for a 100 pack on Amazon, so not as cheap as normal cage nuts, but will save a ton of swearing and pinched fingers. Did a new rack last month with these and loved them.
I think about 3 1/2" or 4", just grabbed something that had a big enough head to cover the mounting hole without that cheap washer that came with it out of the bulk bins.
Really can't understand why they would want you to drill into a stud and use an anchor instead of just a lag bolt for this...
Just did those same cabinets a few weeks ago, the mounting hardware it came with is junk. I went back and grabbed some lag bolts instead.. much more secure, throw those anchors away.
I had a few odd spots where I could only hit 1 stud due to the 30" rail and 16" centered studs, used a zip...