I am not CSV user, but - if anyone says me that Inline::C does not give you enough performance - then there is something wrong with implementation.

How come some XS module utilizes Inline::C?? When you're using XS - you already at C level. What a design requires you to use Inline::C

Therefore your sentence about performance is not convincing, and even - other way round - I now suspect there's something hidden in calculation here.