Thanks for the advice.
I changed the bush over the weekend, following the advice in one of the other forums- cut out the central rubber & then cut the steel sleeve on the original bush.
The powerflex bush went in very easily by hand with a tap on the worksurface to make sure both sides were well home. Since the Powerflex bush protrudes from the dogbone, it's a trickier to get into the mount. It went in OK once I'd shortened the link so I could get the small end over it's mount.
On driving there is a little more noise transmitted, mostly during acceleration, but it's not particularly noticeable & sounds kinda sporty anyway. Unfortunately, I haven't gotten on a motorway properly yet to see what noise is transmitted at speed.
(the only bit of the M5 I've been on has a 40 limit
did get some interest from some guys in a Rover 200 convertible though
not sure if they were impressed by the car or wanted a race
A couple of things that surprise me are that the gearshift seems to be improved noticeably & the steering appears very slightly more precise.
I think a little adjustment is called for, to see if the noise is due to the link being overlong, but other than that I think I'm happy with it.