If your ground phase is in the 40's with the concentric coil, I'd say your soil has a moderate level of magnetic mineralization and the concentric coils should work fine. If you've read many of my posts on any of these forums, you know I am not a big fan of the pre-programmed discrimination mode number 2. Simply too many good targets being passed up with that level of discrimination. Pattern one isn't so bad, unless you are working an area with lots of iron trash and would like to work out the adjacent coins. Then I prefer to hear the low tones opposed to nulling (on the ferrous targets). Simply a matter of personal preference.
If you are an experienced detectorist, I won't go into the technical aspects of sweep speed or coil placement. But I would suggest you take a TID reading on those pull tabs after you dig them up and see if they still read the same as when they were buried. If they do, and they happen to read the same TID as some of the coins you are looking for, then there is little you can do to not dig them if you are simply going by TID numbers. As you know, the TID is an electronic display of the target's conductive properties, based on the software's interpretation of the return phase. I know I have a problem with Pepsi screw caps. Coca Cola caps don't pose a problem. But those darn aluminum Pepsi caps fool me into thinking they are a quarter all the time. However, on the pull tabs, if you listen carefully, there is typically a subtle difference in the tonal quality of the audio response. Since they are not round, pull tabs are not usually consistent in tone when sweeping from various directions. It is important, however, to use multiple tone audio (28 tones) when listening for the broken sounds. Using 2 tone or 4 tone will not provide the variations that you can hear with multiple tone.
Don't get discouraged, I've used just about every Fisher since the 555 back in the early 80's, and every Tesoro since my first original Silver Sabre in the mid-80's. And I can say without hesitation that I prefer my 705 hands-down. It looks quite simple to operate. And for the most part, it is. But to truly understand how to maximize its potential, you need to learn to "hear" what it is "saying", and not rely on TID numbers. Learn to hunt by ear and use the numbers merely to give you a headsup as to what to expect to find in the hole. Take one of your Tesoros or Fishers along on your next hunt and do some comparisons. Grid off an area and hunt it with one detector, marking the targets with golf tees or poker chips. Take notes on what you think each target will be. Then hunt it with the other detector, confirming each target you hit the first time, and marking any new ones with a different colored marker. When you get done detecting, dig up the targets and compare the results to your notes. I think you'll find that the skills you are using to distinguish pull tabs on your other detectors are same skills you will need with the X-TERRA. Just a matter of listening for the right sounds. JMHO HH Randy