I have had the 705 for a few months now. Its a good machine. I have a number of the coils for it and have found that each will have its use depending on what you are hunting for and where. Out here in Colorado we have a pretty high amount of mineralization. It does vary from location to location though. I have found that the older towns/older neighborhoods have alot less. Why that is, I have no idea.
But if you have already ordered your 705, then you havent made a mistake. If you havent ordered it yet. Then dont worry. You are getting a good machine. This is coming from a guy who has owned a large number of different brands and kinds of machines over the years. And still own more than one. The 705 is good in that you can select your coil and frequency for the location and type of target you are hunting. Now having said that, I would rather minelab had made it possible to change frequency at the controls rather than having to change coils. They could have done the electronics to do that fairly simply. Of course, they wouldnt have made the extra money selling X-terra owners the extra coils.
You will need to invest in at least one or two other coils. I dont recall you mentioning if you are buying yours with just one coil or getting a multi coil package. If you can, get at least a 2 coil package and then save your bucks to get a third down the road. You should have one for each frequency and if you are hunting for a particular target, then maybe several in the frequency that is best for that target. I have 3 coils in the high freq and 2 in the medium. Still have to get the low freq coil. One of the first extra you get should be one of the small 6 inch in ether the medium or high freade the purchaseq. The medium freq one would likely be the best unless you are going to be hunting alot for gold. The 6 inch will help you alot when you are hunting in areas with a high concentration of junk and with getting closer to fences and other obstructions. The six inch helps you get in between the junk to find the good stuff. Anyway, now that I have you totally confused...

I hope not...but I do hope you get the 705, and I think someone mentioned maybe you getting the 505..and he is right to an extent...the extra bells and whistles is what I liked about the 705. But thats me. Good luck and I hope you get it soon and get out there finding the treasure.