i take default exhaust off, and make new cat forward. I put 2 inches mufler because of the little space for a cardan and went on 2.5inch the rest of the exhaust. is that cat -> 2inch ->2.5inch bad idea. is too much distressed ?

v70 mk2, 2.5t awd

 

going from 2.5 inch pipe to a 2.0 in pipe will cut your flow rate by almost 40%. It's like going from a "5" to "3". Considering an engine is an air pump, if you need a 5 to produce your top HP (lets say your V70 makes 200 HP) and you can only pump through 3 of the 5, your max HP will be about 120 before you start building up abnormal back pressure... in short, a really bad idea.