I upgraded my ultimaker 2 to 2+ with the extrusion kit. Then after one week of printing I faced a problem in the inner gear (smaller 11-teeth one). It seems that to feeder motor shaft was rotating loosely inside the gear so that the gear itself was not rotating. That resulted in massive under-extrusions. So I printed it.
PLA is not strong enough. For me I used Colorfabb XT with excellent results. I did not try ABS but I think it will be ok.
Also, scale the X and Y to account for shrinking ( 1% for colorfabb XT, 3% for PLA)