ok - had my rear-end rebuilt today - went from 3.27 to 3.73, new bearings, new clutches, bushes replaced.
Here are the bushes from the front of the IRS (used) and the bushes from the subframe (not replaced). The bush from the rear of the IRS isn't shown as they have to be cut out (I should have photographed it first - sorry) - however. according to the invoice, they were pretty cheap when I got them a few years back:
The front pair of bushes were ok, but they replaced them anyway. The rear bush was pretty flogged out (the one that they melted & cut out) so I'll let you know if I notice any change in driving experience (other than the fact that 1st is now normal, 6th is now 1,950rpm at 100kph) relating to the IRS being more tightly controlled.