I've found that it is all down to how the garage takes the emmissions test, which will determine if these cars pass or fail... As just left on tick over they are likely to be just over, but the testing station should be able to rev the to something like 1500rpm during a portion of the test.. but many places find this difficult to do or don't bother.
My local garage always manages to get all our cars through, without breaking any rules.. and quite likes it when we take the 993, as he has to road test it for the brake test, as its four wheel drive..
Big garages and chains basically don't care about repeat business, where as the smaller outfits and specialist want you to come back so are not normally there just to make the fast buck.
If I was you I would talk to the testers at the OPC or look further afield
Adam.