Box is fine, don't know why you think its a weak link tbh.
Link: http://www.cliosport.net/forum/showthread.php?t=473561
The box is well known to be the wink link on the 197 because its a shit box. Hence why so many people have had problems and lots of gearboxes have been replaced.
Im sure ive been told that its a six speed gear box out of a dog end diesel laguna so no wonder it cant handle the power as is.
If your talking about turbo'ing the clio you need to talk about stand alone management, LSD, gearbox, clutch and suspension to get the most out of it. Yes it is a great car but it wasnt designed to handle anywhere near 250bhp.
PROBLEMS PROBLEMS PROBLEMS