As you may know, it is very hard for any detector to ID very deep, old coins correctly. Many older coins will fall out of the coin range, especially copper, bass and bronze, when at greater depths. This is were the 3d is different in the enhanced mode. The 3d chances the way it ID"s items by moving or bumping up the ID's..so to speak. This is a great thing and again takes some of the guess work out of the iffy signals that would normally fall or bounce in a lower ID range. But here is the draw back in local parks, It will make the can slaw, and some of the older pull tabs read in the coin range. With a lack of a better term, it make the detector more sensitive to some items. These items will fool you at times until you learn the sounds, and read in the high coin range. A lot of it will come with learning to size the item and listening to the tones closer, as well as pinpointing sounds to name a few. I am sure someone on here could explain it much better than myself, but I did feel you deserved a answer. On the other side, larger gold rings and gold coins read as a high coin ID were most read them as trash. Some have no trouble with using the enhanced mode in parks, others hate to dig the trash and like better discrimination against junk. Myself, I never use discrimination anyway...all metal or no rejecting is the way to hunt. I would only recommed getting the 3d for the use of the enhanced mode, what it was designed for. If you don't feel you will use that mode often...then I would keep looking.
Out of respect I should mention again, I have never used the minelab sov. that you asked about, but I have heard many wonderful things about the depth of that detector. What the learning curve is or your experience should be considered. My best advice...see about renting or borrowing both of these machines and give them a try. Most here will admit, no one machine does it all....that is why most of us have a few detectors for different hunting locations and conditions. Good luck.