Finally got round to fitting the new cable yesterday. Mixed up the carb tops (rear one has the tighter bend to clear the frame), then the fuel pipes too (rear one is the lower one).
All back together - no difference. Heavy throttle that doesn't return on its own. Arse.
After a test ride that didn't fix the problem, I pulled it apart again at the handlebar end. And discovered that the twistgrip was glued to the bar with dried grease and a bit of corrosion. Cleaned it up, squirt of light oil under the grip, sorted.
So, to answer my original question, either style of cable will work OK, but check the simpler stuff first...
