hi,
im a builder / developer...
unfortunatly i havent used sip's....and cannot fully comment.....
but would you really save that much on space by using this method?...a traditional brick / cavity / block construction would only be 280mm wide if the correct cavity insulation was used
granted you would potentially save some time on erection, but unless time is very critical to you, i would say the increased cost of using the system would not be worth it.
have you looked at timber frame?...again not much cavity width saving, but quick to erect and well insulated.
i would invest wisely in the services of a thorough geotechnical consultant ( with trial / boreholes ) to ascertain the most cost effective foundation solution....and use your saved money on the build.
i can put you in touch with one if you require.....and if necessary i have a friend that is a drilling and grouting specialist that travels nationwide and is very reasonable.
sounds like you grouted a seam or a shaft on your last job!....i had a job where we were grouting for 12 weeks solid.....thousands of tonnes of PFA went in.....ouch!
good luck!