Ropes sound like a great solution for various text editing problems in Squeak. 
I would love to see them working.

It's the sort of idea that makes you think "I've thought of something like 
that before, except for *that* bit... cool".

About the performance tuning - another approach would be to do an actual 
performance test at runtime (first time a string is created after the image is 
opened...) to determine the relative costs of these operations in the 
particular configuration.

Daniel