You're talking about a difference of 25-40 Watts of rated power, of which the amplifier's efficiency is already reducing, plus this is at 14.4V. The theoretical difference in output measured in decibels when comparing 60 Watts to 100 Watts is an increase of only 2.4 dB. This is audible but it's not enough to make you think, "Wow, I'm glad I got the bigger amp". It's a difference of a few more clicks on the volume.
The real danger is excessive heat over time, which is caused by playing music into clipping levels. There can be massive differences in music levels depending on how it was originally mixed and what was done to that music by the time it got to your head unit.