Interesting problem that I also don't have a solution to. I think removing roman numerals above number 5000 will be the best way to deal with.

But still I found a way to add overlines like this, so why not:

  • 5407 ==> VCDVII
  • 157897 ==> CLVMMDCCCXCVII

This is also very useful for representing rational numbers that have repeating digits such as this:

  • 1/31 = 0.032258064516129

I added the template Template:Overline for this.

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