I've just bought a set of IRS bushes, not control arm bushes, but the kit for the cradle, the life expectancy of the OEM rubber bushes is about 10 years/100K's apparently...
There are a couple of interesting quirks (I've not done mine yet) as the cradle is held on to the chassis at the front by 2 x 12mm bolts. The holes in the cradle and the frame are 14mm....
The kit has 2 x 14mm bolts (same thread size) and harder bushes. I have the bushes for the diff centre/cradle mounts too - I'm trying to remove some of the Cobra "thunk" as you get on/off the gas, it's a common complaint.
I seem to have a lot of play in my half-shafts when comparing one side to another, according to my mechanic, but I'll get the bushes done first and see what changes...