Tough call on which Minelab to buy, but I'd take the 705 over the Safari. The main reason is that I don't think that the Safari is enough different for the $.
There is a BIG difference in the technology employed, but the Xterra can be tailored for speciffic targets, and can be swung over ground that is nearly un-huntable with an FBS machine.
I've been hunting old homesites with both an XT-705 and an Explorer SE, and the Explorer is about useless at some sites. The 705 on the other hand, has produced quite well, and handles iron trash impressivley with a 3kHz coil on. The new Coiltek 6" 3kHz sorts through trash and slams on copper and silver like no other.