Two twin-screw extruders of different size and centerline distance C-L were compared. To understand better the performance of the extruders, the operation points were optimized for an HDPE (high-density polyethylene) film product, and the performance of screw configuration was qualitatively analyzed with some numerical methods at the operation points. The machinery with narrower C-L was found to have lower average shear rate, higher conveying capacity, and more channeling in the conveying flow. That means also a need for severe processing in the kneading zone. The extruder with narrow C-L had a narrow operation window, and that made it more difficult to combine homogenization and degradation of the product.