The extra space in over-provisioning should increase Available Reserved Space as well, right? If the ARS = 1, you should be able to OP by 4GB and get it back to 100...

I've heard that some controllers don't use the extra space in over-provisioning in this manner. With the Intel's, you should get some performance benefit just from not using all the available space for your partition, though I'm unclear on whether the drive makes some sort of distinction between real spare area and unallocated space on the drive.

Since I don't really need much space, every drive I'm using gets OP'd now (even though I surely don't need to, but it's probably not a bad practice). I could OP my 128GB drives down to 40GB and still have plenty of space for most of my system images.