I've had the Xterra since 2013, it was the first detector I ever bought and it has been my main detector since then. I've tried others and kept others, but the 705 still gets the job done. The 10.5 MF 7.5khz DD coil rarely leaves my detector and has the best response on targets in general, in my opinion. The 3Khz really struggles with nickels and lower conductors, as does the MF, but it'll find em better than LF 3Khz. Also, the 6in HF 18.75 coil is a must have for jewelry hunting in parks. It's smaller than your 10x5, but it's light and plenty deep. I never needed a coil larger then the 10.5 MF. And keep the 9in. Concentrics are very different than DDs and are deeper coils in general than DDs in low to mildly mineralized soil. You'll regret selling it down the road once you realize you actually need it and have to spend more money on one.
Also, I always run in all-metal. Rarely do I ever run in Disc mode. Only when the trash is too abundant do i add some disc. Something I also like to do is run it in prospecting mode, then once you get a target, click over to all metal to quickly get an idea if it's an iron signal then click back over to prospecting mode. That's my primary search method when I'm relic hunting.