On the upgrade select screen scroll through the Kongpanians. If you've earned any on the Kong website (normal and shiny) you can get a bigger X2 and X3 upgrade bonus.
That last ball was by far the hardest factory ball out of all series. Immensely satisfying to complete though.
Great job Mr Bonte - I hope you make more.
Excellent game - very clever. Shame a glitch causes sticky keys which causes me to repeatedly run to my death. Given up on getting the two harder badges.