Flown C172's for quite a while, and never had anybody in the back.
Now I'm planning on quite a trip, with 2 pax and luggage.

When I fill the fuel to the *tabs*, calc everyone's weight honestly and
consider baggage -- I'm 75 lbs over the 2450 gross on departure. Maybe
100 over gross if I assume a "lie about weight" factor or some
inaccuracy with filling the tanks. Now I'm scratching my head about
just how risky this is. I know (others) have pushed over gross in these
planes way more under worse conditions, and have almost always gotten
away with it. I'm inclined to just do it, and be cognizant that it will
perform differently, i.e. don't expect the same picture on climbout that
you would when solo.

Risky? Or just roundoff error on the weight? Here are some other factors:

This is the 160HP C172, standard.
Departure runway is 5000'.
No steep terrain to climb out of.
Plenty of alternates along with the way with 3000 runways.
Not particularly hot, humid, or high. 50 degrees at 1000 MSL for
departure or any point of landing.

I'm figuring I'm 3% over gross, causing most of my V speeds to increase
1.5%, so say -- instead of flying short final at 65 knots, I'd fly at 66
knots... OK wait I can't hold airspeed to +/- 1 knot on most days anyways.

I'm thinking through many of the factors, and it is only a "little" over
gross, only on the first hour or so of the trip. What else should I be
aware of? Am I dangerous?

T