I've owned several MXT's, field tested the first release of X-Terras and purchased a new X-705 this summer. First off, let me say that both the MXT and 705 are excellent detectors made by reputable companies. And, both are capable of providing years of enjoyment. Although there are many similarities, (coin mode, prospecting mode, threshold, display etc) there are some differences that I really like on the X-Terra. For example, I prefer notch discrimination over variable discrimination. Especially if I am hunting nasty trashy areas with an abundance of can slaw. I can eliminate a good portion of the trash by notching out a segment or two on the X-Terra, without fear of missing too many "goodies". On the other hand, if I were to set the discrimination to eliminate the same trashy targets with the MXT, I'd also be discriminating out several types of US coins, as well as much of the gold jewelry. I prefer to hunt with more than one tone. On the MXT, I can go to relic mode and have two tones. But in the Coin/Jewelry mode, I'm stuck with one tone for all targets that are set to be accepted. This requires me to be more aware of the TID instead of relying on my ears, ,as I can with the X-Terra. On the 705, I have my choice of one tone, two tones, three tones, four tones or 28 tones. Having 28 tones represents a different audio tone for each notch segment. Granted, the MXT offers a much wider range of TID numbers. But if I know the notch segment that certain coins are going to hit, what is the point in having such a wide range? Frankly, if it looks good on either machine, (or simply sounds good on the X-Terra) I'll be digging it regardless of the exact TID number. (or the White's icon)
The sites I hunt are moderately mineralized, for the most part. However, there is a wide range of mineralization within "moderate". While both models allow me to "track" the ground, the X-Terra also allows me to hunt in manual GB or offset my GB to be either positive or negative. Plus, since you mentioned hunting a beach or two, the X-Terra offers a specific Beach mode for maintining a proper GB at those sites. Although the 14 kHz of the MXT is somewhat universal in it's applications. It will find coins and jewelry. However, I like the ability to switch coils, thus switch operating frequency, on the X-Terra. The stock 9 inch concentric coil at 7.5 kHz is a good all-around coil for a coinshooter or a relic hunter. I personally prefer the 3 kHz concentric for hunting open sites in search of old silver and copper coins. And I like the small DD coil at 18.75 kHz for sniping coins and jewelry in trashy areas. Although my soil conditions don't warrant the use of the larger 10.5 DD, there are many who are having tremendous success with it. Add all this to the weight, balance, backlight, Noise cancel channels and the ability to operate at one of three frequencies and you have the 705. Like I said, both are great detectors and either one should serve you well. Depth-wise, I don't see much (if any) difference when using comparible sized coils. Sensitivity to small targets? I give that nod to the X-Terra. And I attribute much of that to the fast processing of the X-Terra, and it's forgiving +/- sweep speed. JMHO HH Randy