Probably nothing to worth worrying about in the iron range if mainly after coins/jewellery, some very small gold items may hit towards the iron range, though a majority of rings will read higher ID's.
It's purely personal preference on listening to iron or discriminating it out, it will drive some people nuts with constant low tones going off all the time, whilst others are prepared to put up with it, and try to pick out the high tones from amongst the mix. Probably easier to just knock the iron out to start with. On the upside, iron can indicate areas of previous habitation or activity, and hence may prove to be good older locations to search for coins in.
Very deep targets may also be mistakely indentified as iron due to being out of effective range of both discrimination and detector capability. If in doubt on some of those dodgy sounding targets, better off to dig them at first to see what they are, and make a mental note for next time round if continually coming up as junk finds.
Also wind the sensitivity back if just after spendables, no point in listening to every target in the soil if you are just after shallow modern coinage, and use the DD coil in the junkier areas, much easier to separate out targets with vs the concentric.
If I were to purchase a 705, I'd be looking at owning the 10" DD coil for general detecting duties, as the supplied coils are a bit of a compromise for those choosing to do a bit of gold & coin detecting.
