Well first of all it depends if they exceeded the 105kg, or that they just had more fuel in the tank than they rapported to the FIA (e.g. rapported 100kg, while 104.88kg was in the tank).
Given 105kg is the maximum, it is at the very least 4.64% more fuel. I'd say significant yes. It'll allow for more fuel to be burned and therefore less lift and coast.
For the record, I am correct to assume this is a breach of the technical regulations right? Or is it sporting regulations?