Ceiling -- finishing query / problem`

I have two ceilings to finish off that were plasterboarded (9.5mm) taped with the self adhesive fibreglass netting tape and badly filled (overfilled) with Easy-fill. This was some months ago and it seems to have gone rock hard now, whereas freshly Easyfilled is a doddle to rub down. I have tried mechanical sanders but its just going to take too long - question is, what are the options ?
I have dry-lined walls quite successfully, but not done ceilings and the guy who did these fell ill and is no longer around, leaving me to pick up the problems.
I would have preferred a plain smooth finish but this seems to not be an option unless I get a plasterer in to put about a 2 mm skim over the whole lot, so I am considering Artex-ing it all, but have never done this. Each ceiling is about 4M by 4M and was wondering if this is a good option and any tips ?

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