How noticeable would 5% be anyway? If someone wasn't expecting this power update and got it in their car after, would they notice?
I think it'll be noticeable but not night-and-day. Sort of like the difference between having a passenger in your car vs. not. I expect it to be more noticeable during freeway passing maneuvers than off the line, but you never know.
When the update came out, there were a lot of reports at reddit to the effect of "Yeah I can definitely feel the difference! Much better off the line!" so I think if you EXPECT to feel a difference, you'll feel it whether it's there or not.
Thus far we have no actual evidence that the performance increase was part of this week's update. Hell I thought my P3D- seemed quicker past 50mph but the placebo effect is a powerful thing. Without a tweet from Elon or solid before/after measurements we have no way to be sure.