It has a index clustering operation but this is a one-time operation that will not affect further inserts/updates.

But it shouldn't matter, the implicit constraint on a VARCHAR(n) does not affect indexing.

Interesting, I was just thinking about a variable width item on the disk expanding or contracting, and if it had to be arranged in a serial physical order it would (necessarily) be forced to move the other bits if it wasn't inserted at the end.