Rondoutcreek , detectors with very fast recover speeds seem to do better at picking up targets in the heavy iron but those detectors usually don't go very deep. those detectors generally don't have the better discrimination as the higher end models and because they have the faster recovery they often don't detect as deep as the higher end ones either . so they find the shallow targets in the iron but leave the deepers ones so you might need two types of machines because i don't think theres just one out there now that does it all .
there are a couple of machines that come to mind (remember these are my opinions only) the mxt pro has a great recovery speeds and has proven itself to be s formidable relic detector , i've personally seen the ctx3030 and e-trac find good targets in iron infested areas , i've been hearing about the ATgold and its super fast recover speed too.
As John pointed out the more cappable you are with any particular machine the better you are able to pick out the goods in the iron.
I've been using a dfx for 7 years around these cellars and do pretty well , i like it because i can go from its normal filters 3-6 when doing fields to find the deeper targets and still switch it to 2 filters around cellars foundations to pick out some hiding around the iron. coils make a huge difference in searching around these sites too.
Dan